Practical pathology

1. Autopsies on Animals. In the case of the small animals used ordinarily for laboratory purposes, such as the mouse, rat, guinea-pig, rabbit, cat and dog, the animal is put upon its back and fastened to the autopsy-board either by small nails driven through the extremities or by slip-knots of string or rope passed over the latter. Autopsy board and holders designed especially for the purpose can be obtained from makers of laboratory apparatus. A main-incision is made in the anterior or median line from the chin to the genitalia, and the skin stripped back from the thorax on each side to expose the ribs. The thoracic cavity is then opened by cutting the ribs with the bone-shears or bone-forceps, and the sternum and cartilages are removed. The neck, thoracic and abdominal organs may then be removed en masse and examined outside the body, or the organs may be removed singly and examined in succession, following in general the same methods of procedure as in the autopsy on the human body, adapting the methods given above to differences in anatomic structure and size. For the opening of the skull and spinal canal the bone-forceps alone may be used, or in the case of larger animals the saw may be needed. Anatomic considerations should govern the method of opening the skull. Directions for the performance of autopsies on inoculated animals will be found in textbooks on bacteriology; and veterinary methods of autopsies on the larger domestic animals are given in textbooks on veterinary pathology. In all cases of autopsies on animals full protocols should be kept, following the general order of the autopsy, altered to suit the individual case.

2. Surgical Operation. A very large part of the material obtained for pathologic examination is removed by the surgeon for diagnostic purposes. The question of the surgical technique employed may be left to the surgeon, but as far as the pathologic aim is concerned certain principles should be followed, if the object of the examination is to be secured. Unfortunately these principles are not recognized by the great majority of practitioners, and pieces of tissue to be examined are taken at haphazard from the surface or from necrotic areas, to be run through by the pathologist, only to find that no diagnosis is possible, either because the portion of tissue removed did not extend deeply enough or is wholly necrotic. Great care and judgment should be exercised in the choice of the portions to be removed for diagnosis. The part removed must be characteristic of the condition present. It is necessary not only to ascertain the character of the pathologic change but also the nature of the reaction in the surrounding tissue. A neoplasm may show the histologic structure of an adenoma, but at its periphery may be found infiltrating the neighboring tissues as an adenocarcinoma. If the piece of tissue for examination is removed from the central part or surface of the tumor, an incorrect diagnosis may be given. This is especially true in the case of rectal and uterine polypi, papillomata of the mouth and penis, horny warts, etc. The rule to be followed in all cases is that the excised portion must be at the boundary-line of the neoplasm or morbid process, and extending across it so as to include both pathologic and surrounding normal tissues. The cut must be deep enough to extend into living tissue, and in the case of epithelial surfaces to go below the basement membrane. It should be made at right angles to the surface. Necrotic, softened, or degenerating portions should be avoided, unless a portion of this is removed in addition for the purpose of ascertaining the nature of the degenerative changes present. The scraping away of superficial scabs, exudates, etc., should never be practiced for purposes of diagnosis. Time is saved if a satisfactory excision be made the first time, and to secure this the tissue must be living, the cut must be deep enough, and the portion removed must fully represent the nature of the condition present. When organs are removed, as in the case of the appendix, uterus, tubes, ovaries, mamma, etc., several portions of tissue representing different structures of the organ should be secured for the examination.

Tumors and other pathologic specimens received from the surgeon should be fully described as to size, form, weight, consistence, color, relation to surrounding tissues (encapsulated, well-defined borders, growth by infiltration or expansion, zone of inflammation, etc.), character of cut-surface (color, moisture, translucency, smooth or elevated, homogeneous, character of cell-scraping, evidences of structure, etc.). Accompanying all pathologic material sent to the pathologist should be concise and accurate notes giving the name, sex, age, nationality, occupation and status of the patient, anything in the individual or family history bearing upon the condition, the source of the specimen, its exact location and relations, manner of growth and character of operation. The pathologist should have full data upon which to construct his diagnosis. A very common idea among surgeons is that the specimen alone should be sufficient for the pathologist, and that other data are not necessary for the formation of his opinion. Many other considerations than the mere histologic picture presented by a specimen enter into the formulation of a pathologic diagnosis, if it is to bring to the aid of the surgeon all that a pathologist’s knowledge and experience can give. This is particularly true when the pathologist, as is usually the case, is asked to give a prognosis. Both in hospital service and in private surgical practice it is best to have printed history forms to be filled out and to be sent to the pathologist with each specimen.

Another factor seriously interfering with the efficiency of the pathologist’s work is the failure of the surgeon to see that the material removed for diagnosis is properly taken care of before it reaches the pathologist. Tissues removed for examination should never be allowed to dry. They should not be exposed to the air, but should either be placed at once in a fixing fluid or covered with damp cloth. Curettings should be placed for a moment upon a pad of gauze to remove the excess of blood, and the fragments of tissue are then picked up and put into the fixing solution. When sent by mail or express fresh tissues should be wrapped in damp cloth and then in rubber cloth; or if the distance is great they should be put into fixing fluids. A sufficient quantity of the latter should be used, or decomposition may take place before the specimen reaches the pathologist. All material for bacteriologic examination should be removed under proper precautions, put into sterilized vessels, properly sealed and sent to the pathologist under proper precautions.