The principles and practice of modern surgery

Inflammation is an expression of the effort made by a given organism to rid itself of or render inert noxious irritants, arising from within or introduced from without (Sutton, modified).

After having duly considered hyperemia as a phenomenon having an identity and termination of its own, we are prepared to study the more complex processes included under the term inflammation, the first of which is the hyperemia already considered. The characteristic of the truly inflammatory process is that it does not stop with mere congestion nor with any of its previously mentioned terminations, but goes on to something more complex. It must be understood, therefore, in this consideration that hyperemia is the first act of the vessels, resulting from peculiar stimuli which will shortly be considered. Even the hyperemia seems to be now more distinct than under other circumstances, and, along with the dilatation of vessels and the stagnation of blood current, the capillary vessels seem crowded with blood corpuscles to an abnormal degree, the rapidity of their motion is checked, and there occurs accumulation of blood cells along the walls of the small veins, to which they seem to adhere as if by some new cohesive property. The result is that before long the vessel wall appears to have received a new coating of white corpuscles, this being more marked in the veins than in the arterioles, while in the latter the red are more numerously mingled with the white than in the veins, in which the distinction between the two classes of cells is better maintained.

Next comes the phenomenon whose clear recognition and description is inseparably connected with Cohnheim’s name. This is known under different names as migration or diapedesis of the leukocytes. The program is about as follows: A little protrusion of the vascular wall, a marked alteration in the shape of a leukocyte, which yet adheres to this point of its lumen, and then the curious fact so often seen under the microscope—the gradual passage of this cell through the vascular wall, from its inner to its outer side, by what is generally known as its ameboid movement. This migration of the leukocyte is not confined to its mere escape from the restriction of the vessel lumen, but goes on to an indeterminate extent after it has detached itself from the outer surface of the vessel. This seems to occur by virtue of the same ameboid characteristic which it exhibited in passing through between the cells of the vessel itself. If this occurs at one point, it occurs at innumerable points, in consequence of which a large number of leukocytes escape into the tissues of the part involved. This diapedesis occurs most markedly from the smaller veins, to a less extent from the capillaries. The cells which escape from the latter are usually accompanied by red cells, the consequence being that the exudate which necessarily occurs at the same time is more or less tinged with the coloring matter of the blood, and is known as a hemorrhagic exudate.

The above phenomenon, described in so few words, is in its minutiæ a really complex one, depending on a variety of causes not easily appreciated; but it is at least positive and well known, because it can be observed at will in the mesentery or web or tongue of certain animals which can be confined upon the stage of the microscope. The phenomena of inflammation, therefore, comprise, first, hyperemia, and then escape from the bloodvessels of the corpuscular and fluid elements of the blood. The former may be due, as already seen, to various irritations of a non-specific character; while, as we shall learn, the latter practically never take place save when the irritation has been, as pathologists say, specific or infectious.

The phenomena of true inflammation comprise practically the roles played by the three elements which conspire to produce those changes—namely, the tissues, the blood, and the specific irritants which are the primary cause of the entire lesion. Each of these should be considered separately.

All observers agree that in actively inflamed tissues the number of cells is very greatly increased. A certain increase may be accounted for by that which has already been described—namely, the escape into the tissues of the wandering cells from the bloodvessels. But neither this alone nor the products of their rapid proliferation are sufficient to account for all the cells found in the truly inflammatory condition. It is now well established that in connective tissue there are two varieties of cells—the fixed and the wandering—the former concealed in the trabeculæ of the intercellular substance, while the latter are small, ordinarily round in shape, much resembling the white corpuscles, possessed of ameboid characteristics, and having the power of changing position. These are known as the wandering cells, which meander through the lymph spaces of the tissues or back and forth into and out of the blood-vascular system, their migration being regulated by causes not yet known. Under natural conditions their number is relatively small. Once given a true inflammatory disturbance they are reproduced with amazing rapidity; and their numbers, added to those produced by diapedesis of leukocytes, with the combined proliferative activity of both forms, serve to account for the new cells whose presence characterizes phlegmonous and other similar disturbances. That these wandering connective-tissue cells have much to do with these changes is shown by the unmistakable evidences of excessive activity known as karyokinesis (i. e., nuclear activity).

Karyokinesis is common not only in inflammatory disturbances, but in new-growths of rapid formation, especially sarcomas, which are formed from mesoblastic cells, the same which have to do with connective tissue. Endothelial cells also undergo the same changes.

The peculiar characteristics of the leukocytes have already been described at considerable length in the preceding chapter. It must suffice, then, here to say that during the inflammatory attack the leukocytes are increased in number, i. e., there is a temporary leukocytosis which is the usual accompaniment of suppuration. For instance, this is regularly present in purulent, but not in catarrhal, forms of appendicitis. The recognition of this fact may be of great value in diagnosis. For instance, leukocytosis is rarely present in tuberculous disease unless suppuration complicates the case. It is met with in suppurative osteomyelitis and in all cases of pocketing of pus. Moreover, when leukocytosis is present coagulability of the blood is increased. Of the various leukocytes, it is the mononuclear and polynuclear forms (see Chapter II) which are endowed with the most pronounced activity and which play the principal role among the blood cells or phagocytes. That phagocytosis plays a most important part in the inflammatory process is a matter to be emphasized in more than one way and in more than one place. The account of the process already given should suffice for descriptive purposes; the importance of the act, however, should be made most prominent in considering inflammation and suppuration. That the phagocytic properties of these cells are limited will be remembered when we recall that in certain instances phagocytes, which are incapable of defence as against the mature bacterial organism, are yet capable of englobing the spores and preventing their development. Nevertheless, the activities of even the most lively phagocytes are capable of being influenced and repressed by extremes of heat and cold to which patients may be exposed, either locally or generally.

CHEMOTAXIS AND OPSONINS.

Having considered briefly the cells which take prominent part in the inflammatory process, and the escape along with them of the fluid portions of the blood, whether these coagulate or not, it is necessary before referring to specific factors to discuss that which induces the above cells to act in this way. That there is a peculiar, even a mysterious, attraction which brings specific irritant and phagocyte together has been for some time recognized, but it remained for Pfeffer to study it carefully and to give it the name by which it now passes, i. e., chemotaxis, while others have widened our knowledge of it, especially by a recognition of the opsonins or material which “prepares food,” i. e., prepare microbes for ingestion by the phagocytes.

Chemotaxis is a term implying a peculiar property of attraction and repulsion between cells, both animal and vegetable. It mainly pertains to vegetable cells alone, and has been offered as the explanation of the sporulation of ferns, for example; but as it interests us most in this place it is manifested between the animal cells of the human body and the bacteria, which are vegetable cells. As a result the former, i. e., the phagocytes, having power of migration, are drawn toward the latter. To be more accurate, this mutual or peculiar attraction is known as positive chemotaxis, it being also known that exactly the reverse prevails under certain circumstances, and that mobile cells will move away as rapidly as possible from certain organisms or substances for which they seem to have a repugnance, this being known as negative chemotaxis.

SPECIFIC IRRITANTS.

These are essentially living organisms, bacteria, fungi, and the protozoa, the first named being by far the most frequent. Before a lesion can assume the type of inflammation as here understood some one or more of these organisms must have secured an entrance into the tissues, the circumstances determining such invasion being considered a little farther on. It is these living organisms which, having once invaded the tissues, determine that most active congregation and proliferation of certain cells which we have just described under the head of Phagocytosis. When once the irritants are present there begins that very active conflict which Virchow has so graphically alluded to as the battle of the cells. Now the mysterious chemotactic properties of the component substances manifest themselves, and now phagocyte is drawn toward bacterium, or the reverse, while the tiny war goes on with sometimes varying results, it being a question which can prove victor in the conquest. This is no fiction of the imagination, but is a contest which may be seen under the microscope in certain of the lower animals, while its results may be seen in the examination of pus from any human source. In another place I have also likened this conflict to that in which certain of the enemy resort to poisoned weapons, because modern biological chemistry has now shown very evidently that it is a part of the life history of many of these microörganisms to produce, probably as excretory products, albuminoid or other substances having sometimes extremely toxic properties. And so it comes about that in many of the surgical infections, while the local destruction is produced by the actual death of tissues which have been invaded by microörganisms, the general or systemic symptoms, generally referred to as the toxic symptoms, are literally due to poisons generated in the infected area, dispersed throughout the system, and often proving fatal.

The local effect of these specific irritants, when they are not promptly attacked, devoured, and removed by phagocytes, is pus, which means cellular death, or gangrene, which is death of masses of cells which have not had time to separate from each other. Pus, then, is the ordinary consequence of the contest above alluded to, and each pus cell represents the dead body of a phagocyte which has perished in the attempt to protect the parent organism from harm. That it has died valiantly can almost invariably be determined, because within its dead body may be seen one or more of the minute invaders which it has attacked. This, then, is the light in which inflammation and infection should be viewed.

In other words, we may have escape of fluid portions of the blood, which may or may not coagulate; we may even have some escape of corpuscular elements with some activity in the extravascular cells, which shall lead to temporary or even permanent enlargement of a part; all of which may be provoked by injury or by the presence of certain chemical irritants within the blood or tissues; for example, alcohol, uric acid, etc. But the factors which provoke the greatest activity on the part of intravascular and extravascular cells, and which determine the richness in albumin of fluid exudates, or their prompt coagulation as soon as blood serum has escaped from the vessels, and which particularly determine the furious rush of phagocytes and that kind of intercellular conflict which leads many of the contestants on both sides to death, are living organisms which are introduced from without, whose presence at the point of inflammation is abnormal and injurious, which are offending substances in every respect, while the whole phenomenon of inflammation is an expression of an effort to rid the system thereof. Taking this view of the subject, there is an important distinction between hyperemia and its consequences, which is absolutely a non-infectious condition, and inflammation with its consequences, which is always an infection and is always followed by more or less death of cells, the same being often extruded in a semifluid mass known as pus.

CIRCUMSTANCES WHICH FAVOR INFECTION.

1. The Virulence of the Infecting Organisms and the Amount Introduced.

—There is the widest difference between various forms of microörganisms in the matter of virulence; and it is true that there are very great differences between the same species under different circumstances, these differences depending on conditions as yet absolutely unknown. With certain organisms it is enough to infect an animal with one alone in order to bring about a fatal result, this meaning that the organism itself is extremely virulent and the animal extremely susceptible.

In a guinea-pig, for instance, a single virulent anthrax bacillus will produce death, whereas in a more resistant animal many are required, and in still others there is absolute immunity against the disease. Man is much more susceptible to the pyogenic organisms than most of the lower animals, which is one reason why wrong deductions have been drawn from many experiments, and why veterinary surgeons, who are so careless of all antiseptic precautions, as a rule have good results in work which, done after the same fashion on the human being, would be inevitably fatal. It is one reason also why one may draw false inferences from experimental work, for instance, upon dogs, which survive many an operation which can scarcely be successfully repeated upon a human being. The influences which affect the vitality and virulence of microörganisms are most numerous and widespread. Temperature, sunlight, moisture or dryness, association with other bacteria, are but a few of the conditions known to be more or less operative. Inoculation with a small number of certain bacteria may be harmless; up to a certain number it may produce only a local disturbance, like abscess, while a still larger dosage may produce fatal results. This is not the case with all, however, but only with some organisms. Bacteria which have been repeatedly passed through the animal body become more virulent than those cultivated for many generations in test-tubes in the laboratory. This variable virulence is especially characteristic of the colon bacillus, the anthrax bacillus, and the micrococcus of erysipelas. Nor does it always follow that the most virulent organism is necessarily cultivated from the most toxic or serous manifestation of its activity.

2. Association.

—Bacteria are seldom found in pure cultures under natural conditions. By mutual association remarkable changes are produced, sometimes in the direction of enhanced virulence, sometimes in the direction of attenuation of effect. Certain organisms, extremely dangerous alone, lose their power when combined with others, while still others have their virulence increased to a rapidly fatal degree. In fact, these effects are so strange and so contradictory that no law governing them has yet been formulated, it being necessary to establish each case by experimental investigation. The virulence of the anthrax bacillus under ordinary circumstances is well known, as is also that of the streptococcus of erysipelas in man. Yet, when these two organisms are introduced simultaneously, the mixture is apparently wellnigh harmless. On the other hand, the simultaneous inoculation of certain other species greatly increases the danger from either alone. The diplococcus pneumoniæ when combined with the anthrax bacillus seems to have a greatly augmented power.

3. Hereditary Influences.

—The fact that immunity against certain infections and susceptibility to other conditions are transmitted from parent to offspring is one which admits of no dispute. The explanation, however, is almost as remote from us today as it ever was. But the recognition of the fact is of the greatest importance to all practising surgeons. That bacteria frequently enter through wounds and bruises is self-evident, but we all know that such wounds are more likely to suppurate in some than in others, and the causes of infection in some are, to a certain extent, connected with the hereditary habit of tissues. The same causes influence not merely liability to infection, but its severity and character. There are undoubtedly also local as well as general variations, and it is very certain that among these the results of bruising or contusion are by far the most prominent. There is also undoubted experimental evidence that under certain circumstances bacteria produce only local lesions, whereas under others they produce general and even fatal infection.

4. Local Predisposition.

—Local predisposition is a factor of almost equal importance. Once given a distinct infection, and hyperemia is sometimes a contributing cause of inflammation. Per contra, anemia of tissues seems to be also a favoring condition. In parts involved in chronic congestion the blood flows more slowly, while the vessels are dilated and apparently susceptibility is increased. Infection here produces a type of disease mentioned as hypostatic inflammation. Conspicuous exception as to the occasional value of an artificial passive hyperemia is seen, however, in the so-called congestion treatment (Bier’s) of tuberculous joints, where the more or less constant flooding of the tissues with venous blood seems to render them uninhabitable for living bacilli, which apparently die and disappear (by phagocytosis), thus permitting a slow return to the normal condition. General anemia, again, is a predisposing cause, while toxemias, including diabetes, etc., are still more so. The liability of diabetic patients to suppurative and even gangrenous infection is proverbial. The presence of foreign bodies has much to do also, and, infection once having occurred along with its introduction, the presence of a foreign body will nearly always excite suppuration; otherwise it will ordinarily remain inert. The withdrawal of trophic nerve influences also apparently permits infection, as is instanced by the ease with which bed-sores form in paralytic patients. Obstruction to the circulation or to escape of secretions more easily permits infection; for example, in the appendix, in the kidney, in the gall-bladder, the salivary glands, etc. Furthermore, one may formulate a quite comprehensive statement and say that all such lesions as solutions of continuity, hemorrhages, degenerations, vascular stasis produced by strangulation, etc., and all perforations, increase more or less the liability to infection.

5. Pre-existing Disease.

—Here are reckoned, first, previous and long existent toxemias, e. g., syphilis, diabetes, scurvy, etc. Other conditions, like lithemia, cholemia, acetonemia, and the various conditions represented by oxaluria, or in which acetone, peptone, and excess of uric acid are found in the urine, also come under this head. One need never be surprised to find suppuration occurring in those cases in spite of due observance of all ordinary precautions, since by their existence immunity is destroyed and vulnerability increased. (See chapter on Auto-infections.)

Recent toxemias also have important bearing in this same respect. For instance, after typhoid fever and other acute wasting diseases, including the exanthemas, surgical operations are sometimes followed by failure, and should always be postponed until complete recovery, except in cases of emergency. The condition to be hereafter described as enterosepsis, and which has previously been known under many different names, as fecal anemia, stercoremia, etc., is one which makes the performance of all operations dangerous, and which certainly predisposes to septic disturbances of all kinds. The postpuerperal state is also one in which operations are to be avoided if possible.

Certain anatomical changes peculiar to the various ages also belong in this category. Old age, with its accompanying arterial sclerosis, its cardiac debility, and other well-known tissue alterations, favors sluggishness of wound repair and leads not infrequently to sloughing or to bed-sores. Amyloid changes betoken impaired vitality. Children are much more liable to acute osteomyelitis than adults. Nursing infants are apparently exempt from many of the infectious diseases, but possess relatively small power of vital resistance to surgical operations. General anemia and impaired nutrition of the body predispose to most infections and to acute starvation.

6. Personal Habits and Environment.

—Diet has much to do with tissue resistance. Rats fed on bread are more susceptible to anthrax than those fed on meat. Hunger makes pigeons highly susceptible to the same disease, and artificial immunity induced in various animals is quickly destroyed by starvation. Prolonged thirst seems to have the same result. Excessive fatigue generally reduces immunity, as already mentioned. The various drugs which destroy red corpuscles impair immunity, and even by injection of water into the circulation the bactericidal power of the blood is reduced. White mice fed with phloridzin, which produces artificial diabetes, become highly susceptible to glanders, from which they are ordinarily exempt. In this connection may also be mentioned the various toxemias alluded to under the previous heading, which may proceed from the intestine, from the genito-urinary tract, and probably also from other sources. Climate has more or less to do, as also extremes of weather, with power to resist infection or to survive serious operations. Dark habitations, poorly ventilated, constitute surroundings which manifestly predispose to infection of all kinds. Rabbits inoculated with tuberculosis and confined within a dark cell, badly ventilated, become rapidly diseased, while others similarly inoculated, but allowed to roam at large, present but slight evidences of the affection. Certain occupations predispose to certain diseases. This is pre-eminently the case, for example, with workers in mother-of-pearl, who are exceedingly liable to a particular form of osteomyelitis; and with those who make phosphorus matches, who are prone to suffer from a peculiar necrosis of the lower jaw. Prolonged suppuration may produce such changes in the blood and tissues that vital processes of repair, cell resistance, and chemotaxis may be so far interfered with as to facilitate subsequent infection.

Finally, the influence of local injury to tissues, particularly of contusions which cause tissues to lose their vitality, is strenuously insisted upon by all, and is spoken of repeatedly in other places in this work. Many tissues will succumb to inoculation after bruising, ligature en masse, etc., which before such injury are not in the least disturbed.

7. Fetal Infection.

—It is only in a very limited class of cases that infection can be transmitted from mother to fetus, but there are instances of this kind in which the surgeon is deeply concerned. As Welch has stated, syphilis is the only infection capable of direct transmission through the ovum or spermatozoön; but intra-uterine infection may occur in many ways, and many diseases may be thus transmitted. The placenta is usually regarded as a perfect filter; nevertheless, it is occasionally passable to microörganisms. These may be caused by preëxisting lesions in the placenta or by the virulence and activity of bacteria. It is known that in animals the bacilli of chicken cholera (inoculated into the mammalia), of symptomatic anthrax, and the pyogenic cocci, frequently traverse this barrier. In mankind infection in utero has been observed in smallpox, measles, scarlatina, relapsing fever, syphilis, tuberculosis, croupous pneumonia, typhoid fever, anthrax, and surgical sepsis.

SOURCES OF INFECTION.

That the effects of bacterial invasion may be anticipated and guarded against most effectually it is necessary that the practitioner should be thoroughly familiar with the sources from which they come, and the localities in and about the body which they most commonly inhabit or where they are met with in largest numbers.

Skin and Mucous Membranes.

—Of all possible sources of infection, the skin itself is probably the most fertile. It is exposed to contamination by air and by everything which may come in contact with the body, and there is perhaps no organism met with in disease which may not be found upon its surface or within its recesses. In fact, these recesses, such as the crevices beneath the nails, the spaces between the toes, and the various pockets like the tonsils, the axillæ, etc., are those most commonly inhabited by microörganisms.

Bacteria may penetrate the skin by means of three different routes, namely, the sweat glands, the hair follicles, and the sebaceous glands, by means of their regular openings. The hairy appendages of the skin are even greater sources of danger than the skin itself, since a direct path of infection into the depths of the skin is afforded by their follicles. Experimentally it has been shown that when bacteria are rubbed into the skin where there are no follicles, there is freedom from infection, whereas the reverse is equally true, and it is clinically generally recognized that furuncles and carbuncles form almost exclusively in those parts provided with hair and sebaceous glands.

The mucous membranes are in constant contact with microörganisms and furnish conditions in many respects favorable for their rapid development. Nevertheless, the latter is interfered with and often inhibited by certain mechanical and chemical influences which afford protection. The conjunctiva is an extremely exposed membrane, which harbors, however, but a relatively small number of bacteria under ordinary circumstances. The tears before escaping from the conjunctival sac are sterile, and are probably saline enough to act as an antiseptic bath for the cornea. Moreover, by free escape of secretion through the nasal duct the conjunctival sac is kept constantly irrigated, to which is mainly due its ordinary healthy condition, as it is well known how commonly lesions follow obstruction to the lacrymal duct. The horrible results of Egyptian ophthalmia, i. e., the pyogenic form of conjunctivitis, are familiar to travellers in Egypt. Howe and others have shown that this disturbance is due to flies, which are carriers of infection, and are attracted toward the eyes of infants, while the superstitious notions of the parents restrain their children from instinctive protection of the eyes when thus irritated. There is probably no greater common carrier of pyogenic infection than the common house-fly, and nowhere is this agency more demonstrated than in the hot climates of the Orient.

Upper Respiratory Tract.

—The oral cavity and pharynx are seldom free from bacteria. Miller has studied over one hundred species that he has found under various circumstances in the human mouth. Some of these are pathogenic; others are apparently absolutely innocent. Many of the forms which grow in saliva will not grow in ordinary media. (See Plate III, illustrating infection of the teeth.) Miller has also shown that many forms of dental caries are but expressions of bacterial invasion even of those apparently most solid structures, the teeth; and of late we have been taught more fully that such invasion may extend far beyond the confines of the teeth alone, and may spread to various, even to distant parts, and produce possibly fatal mischief. Abscesses in the brain and extensive septic infections have been traced to invasion along the line of the dental tubules. One of the most virulent of all the common inhabitants of the mouth is the pneumococcus of Fränkel, known also as the micrococcus lanceolatus of Stebernrg. In virulence it is a variable organism, but it is present in a virulent state in only 12 or 15 per cent. of cases of infection due to it. This is the organism which is the cause of lobar pneumonia, and frequently of bronchopneumonia, as well as of numerous phlegmons and other inflammations of the throat, and which, getting into the general circulation through the tonsils or other possible ports of entry about the mouth, causes serious septic and inflammatory disturbances in widely distant regions. Aside from dental caries, a widely opened port of entry is often afforded by those ulcerations around the margins of the gums which are produced by accumulations of tartar. Disease in the antrum of Highmore, for instance, and many other local destructions, are frequently caused in this way.

The next most common port of entry is the tonsils, faucial, lingual, and pharyngeal, which contain a variety of crypts which are often filled with secretions or retentions loaded with bacteria. One of the most common sources of an involvement of the cervical lymph nodes in tuberculous disease is an infection springing first from the tonsils or the teeth.

In spite of the fact that myriads of bacteria are swept into the nasal cavities with the air we breathe, few are seen in the nose. A peculiar capsule bacillus, closely allied to that described by Friedländer, has been found in a number of cases of ozena, while the pneumococcus of Fränkel is also often found there, and is known to produce abscesses of the brain. One specific organism—namely, that of rhinoscleroma—concerns the nose almost solely, its first ravages being met with in this location.

Alimentary Canal.

—Probably more microörganisms enter the alimentary canal than gain access in any other way, these coming both from food and drink as well as air. Once within its confines, few of them are capable of prolonged existence. Welch states that the meconium of newborn infants is sterile, but that within twenty-four hours it usually contains abundant bacteria. That bacterial infection through this passage-way is a fertile source of non-surgical lesions is well known. The possibility of surgical infections being produced in the same way is both more remote and less demonstrable. Naturally, anaërobic organisms find here more favorable conditions, and even extremely acid or extremely alkaline conditions do not serve to destroy all such life. Pyogenic cocci are often present and are frequently found in peritoneal exudates. In the intestines of herbivorous animals the tetanus bacilli and those of malignant edema are regularly found. The fungus of actinomycosis also finds its way into the bowel along with ingested food. Under ordinary conditions the bile in its natural reservoirs is free from bacteria, but the colon bacilli and pyogenic cocci often invade these precincts.

Genito-urinary Tract.

—Even the healthy urethra may contain bacteria. While these may wander upward to an indefinite extent, it is believed that the urine contained within the bladder in a condition of perfect health is free from bacteria, and that if such gain entrance they do not long remain. The same is true of the female bladder and urethra. The vagina contains organisms of many species, some of which do not grow on ordinary culture media, but are to be recognized by the microscope. While it is generally acknowledged that the vaginal secretion is, as a rule, possessed of bactericidal properties, there is as yet no satisfactory nor comprehensive explanation of this fact, its normal acidity not being sufficient to account for the fact.

The Milk in the Lacteal Ducts.

—In a condition of perfect health milk secreted from the ideal mammary gland is sterile, but may easily become contaminated upon its exit from the nipple. Conversely, under many favoring conditions organisms may travel into the lacteal ducts from the skin without, and thus contaminate the milk. In all probability the breast corresponds in behavior to other glands whose ducts open upon the surface, and, while such openings invite entrance of bacteria, their migrations do not extend far from the surface unless some of the other conditions already mentioned predispose to further infection or extension.

In summarizing the general topic of possible sources and paths of infection bacteria may enter and exert deleterious action:

• A. From within the system; and
• B. From without.

A. From within they may enter the tissues either through the inspired air, through food and drink, i. e., ingesta, or by means of more direct inoculation, e. g., by foreign bodies or by venereal contact. The danger through infection by inspired air is very small, and concerns probably a limited number of organisms, of which the tubercle bacillus is the most important. Foul air and air which emanates from sewers, cesspools, etc., while most unpleasant to breathe and deleterious in many other ways, do not necessarily contain any microörganisms which can be injurious. This fact, in opposition to general belief, is, nevertheless, proved by recent investigations. The ingesta furnish the most fertile source of contagion from within, but the diseases thereby produced fall for the most part into the domain of medicine rather than that of surgery.

B. Infection from without the body may come by actual contact with previous skin or mucous lesions, and particularly from noxious insects and certain parasites. Among surgeons the principal sources of contact infection to be enumerated and guarded against are:

• 1. Skin and hair;
• 2. Instruments;
• 3. Sponges or their substitutes;
• 4. Suture materials;
• 5. The hands of the surgeon and his assistants;
• 6. Drainage materials;
• 7. Dressing materials;
• 8. From miscellaneous sources, e. g., drops of perspiration, unclean irrigator nozzle, a contaminated nail-brush, the clothing of the operator, etc.

While insisting here upon the recognition of these sources of danger, the precautions to be taken against them are to be considered under another heading, to which the reader is referred.

One of the greatest sources of possible infection has of late been shown to be the presence of flies and other noxious insects, which act as carriers of infection. The Egyptian ophthalmia, which ruins the sight of 30 per cent. of the inhabitants of Egypt, has been shown by Howe and others to be due to infection by this mechanism; and a simple bacteriological experiment will suffice to show that the foot-tracks of a single fly across a wound furnish abundant opportunities for infection with organisms which are presumably virulent. In fact, the danger of carriage of infection by this means is greater than from almost all other sources, except the use of improper materials during surgical operations.

CLASSIFICATION OF INFECTIONS.

We speak of infections as primary, secondary, and mixed; and it is necessary, for purposes of accuracy at least, to make a reasonably clear distinction between them.

Primary Infection.

—By primary infection is meant infection with a single form of organism whose effects are prompt and speedy. Of this, erysipelas or syphilis may serve as illustrations. Most of the acute infections belong to the primary type.

Secondary Infection.

—Secondary infection means that after certain disturbances due to a primary infection, i. e., one of a given type, there occurs at some later period and from a distinct source another infection whose results may be more or less disastrous, and cause the case, at least for the time being, to assume a different aspect. We have an illustration of this in the case, for example, of primary tuberculosis with distinct infection of a number of lymph nodes, which, acting as filters, have caught in their tissue net a large number of tubercle bacilli that, lodging there, have produced the usual well-known results and have practically converted the infected nodes into granulomata. In these infected masses well-known changes, such as those which follow tuberculous infection—atrophy, caseation, calcification, etc.—may be occurring, when suddenly there comes infection of a pyogenic type from another source, and suppuration of the granuloma is the result. It is possible even to have a tertiary infection, of which the following may be a hypothetical instance: Primary infection with scarlatina or measles, by which vital susceptibility is in some instances lowered; as the result of this, secondary tuberculous infection in an individual previously resistant; and, third, a suppurative infection, as above described.

In contradistinction to these distinct events, separated by an appreciable, sometimes a considerable, length of time, we recognize a mixed infection, where two or more organisms are implanted at or about the same time. An illustration of this is seen in most cases of gonorrhea in which there is a synchronous attack made by the gonococcus, which is a specific microörganism, accompanied by staphylococci or streptococci, whose effect will complicate the case and make it assume a less particulate type of infection. Mixed infections may often occur in other ways, as syphilis and chancroid, chancroid and gonorrhea, etc. Most cases of mixed infection belong rather to surgery than to general medicine, and constitute an apparent violation of the rule to which physicians often point—that two distinct infectious diseases are seldom communicated or acquired at the same time. Nevertheless, the facts remain as above.

Terminal Infections.

—Terminal infections constitute an apparent paradox, perhaps oftener in medical than in surgical cases. Few people, as Osler has shown, die of the diseases from which they suffer. The final exitus is due to a more or less rapid infection which terminates life. These terminal infections are mainly due to a few well-known microbes, such as the streptococcus, staphylococcus aureus, pneumococcus, bacillus proteus, gonococcus, bacillus pyocyaneus, and the gas bacillus. In surgery such infections are, perhaps, most often seen in malignant lymphoma, diabetes, tuberculosis, syphilis, cancer, and in the so-called surgical kidney.

BACTERIA OF PUS FORMATION.

Bacteria which act as agents in the formation of pus are collectively known as pyogenic organisms. These are divided into two groups:

• A. The Obligate; and
• B. The Facultative.

Obligate pyogenic organisms are those whose activity is manifested in the direction of pus formation, which seem to produce it if they produce any unpleasant action whatever. On the other hand, the facultative organisms are those which are known occasionally to be active in this direction, and yet which are not always nor necessarily so. The members of group A are fairly well known and catalogued, and are not numerous. On the other hand, there is reason to believe that many organisms may have the occasional effect of producing pus, as it were, by accident or at least in a way not absolutely natural or peculiar to themselves, but still are frequently found when there is no pus present. A suitable list of the facultative organisms, therefore, can hardly be made, and will not be here attempted, the effort being only to mention the more common organisms which play this facultative role. It may be mentioned also that even the adjectives “obligate” and “facultative” are to be accepted with some mental reservation, since staphylococci, for instance, may be met with even in the absence of pus, although nearly all that we know about these organisms implies that pus would be the result of their presence. Furthermore, there are certain other organisms, not, strictly speaking, bacteria, which also have the power of producing either pus or pyoid material. These also will be mentioned in their place. Some of them belong not only to the vegetable, but also to the animal kingdom.

Obligate Pyogenic Organisms.

A. The Staphylococcus Pyogenes Aureus, Albus, Citreus, the Staphylococcus Epidermidis, etc.

—One of the characteristics of the staphylococci as a group is the powerful peptonizing action which they exert. Moreover, the chemical products of their life changes seem to be more potent in a local than a general way, leading to greater destruction of tissue in their immediate vicinity, with greater inhibition of the chemotactic powers of the leukocytes; that is, with more interference with phagocytosis, by which their progress would be interfered with. Their presence is recognized by a peculiar odor, as of sour paste, which should lead to a prompt change of dressings and disinfection of the wound (by irrigation, spraying with hydrogen dioxide, etc.).

B. Streptococcus Pyogenes and Streptococcus Erysipelatis.

—These two organisms do not differ in morphology nor characteristics, and, while for some time considered as distinct from each other, are now by most observers regarded as identical. The streptococci grow in chains of variable length, and individual cocci vary in size. They grow with and without oxygen, in all media, at ordinary temperatures, do not liquefy gelatin, stain readily, sometimes but not invariably coagulate milk, and vary in longevity. They differ extraordinarily in virulence according to their sources.

There are many streptococci not included under the above head which are indistinguishable morphologically and in other respects, and yet which are partly or entirely free from pathogenic activity in man. A biological study reveals remarkable and unexplainable transformation between the different members of this species, a part of which may be referable to conditions pertaining to the organisms infected, but part of which apparently pertains to the bacteria. It is held by some that scarlatina is an invasion by certain organisms of this class; this, however, is not yet definitely established. When found in the stools of children with summer diarrheas they are regarded as indicating ulceration of the intestinal mucosa.

In contradistinction to the staphylococci, the streptococci manifest a predilection for lymph vessels and lymph spaces, along which they extend with great rapidity. They have less peptonizing power than the staphylococci (except in the absence of oxygen); hence streptococcus infection assumes usually the type of widespread infiltration rather than of circumscribed and distinct edema. One sees remarkable instances of this in cases of phlegmonous erysipelas. It is suggested also that the peculiar manner of growth of the streptococci, in long chains which may coil up and entangle blood corpuscles, has much to do with the formation of fat emboli and with pyemic disturbances.

Both these bacterial forms have the power of producing lactic fermentation in milk; and lactic-acid formation sometimes takes place with suppuration in the human tissues, causing acidity of discharge, sour odor, and watery pus. It appears also that these two pyogenic forms have less power of ptomain or toxin formation than many others, and, consequently, that the pyrexia attending suppuration or purulent infiltration is not always to be ascribed to this cause alone, for fever may in some measure be due to tissue metabolism attending their growth, the metabolic products being pyretic. This is in a measure substantiated by the fever attending trichinosis, where the question of ptomain poisoning has not yet been raised.

C. Micrococcus Lanceolatus.

—Micrococcus lanceolatus is also known as the diplococcus pneumoniæ or the pneumococcus of Fränkel and Weichselbaum, and as the micrococcus of sputum septicemia of Pasteur and of Sternberg. It is of interest to surgeons because it causes many localized inflammations and is a frequent factor in causing septicemia; it is often present in the mouths of healthy individuals. It may produce the various forms of exudates as the result of congestion set up by its presence; also otitis media, meningitis, osteomyelitis, and suppurative disturbance in the periosteum, the salivary glands, the thyroid, the kidney, the endocardium, etc.