Metastrongylus apri frequently lives in the bronchial tubes—usually the smaller ones—of the pig309 and wild boar; it is also found occasionally in sheep and in man; in young pigs it is apt to set up a bronchitis, which frequently causes death.

The first communication as to the occurrence of this species in man was that of Diesing, who, in 1845, in Klausenburg, had the opportunity of examining Strongylidæ found by Jortsits in the lung of a little boy, aged 6, in Transylvania; probably also the Nematodes found in the trachea and larynx of man, and described by Rainey and Bristowe as specimens of Filaria trachealis, belong to this group; according to Chatin, Metastrongylus apri may also occur in the intestine of man; this occurrence, however, may in all probability have been due to an accidental introduction of adult worms into the intestine, and should not be attributed to an infection by the larval stage.

No experiments to induce infection have been made; it is probable, however, that infection is direct and without the aid of an intermediate host.

Sub-family. Trichostrongylinæ, Leiper, 1908.

Strongylidæ with buccal capsule absent or slightly developed, vagina short, uteri divergent (i.e., anterior and posterior), ovejectors differentiated. Parasitic in the alimentary canal. Contains the genera Trichostrongylus, Hæmonchus, Ostertagia, Nematodirus, Cooperia, Dictyocaulus.310

Genus. Trichostrongylus, Looss, 1905.

Very small Strongylidæ. Mouth with three small lips and nodular or punctiform papillæ. Cervical papillæ absent. Bursa entirely closed, with large lateral lobes, and median lobe not distinctly defined. Anterior311 rays double, the branches widely divergent, one thin, the other thick, and close to the antero-median. The postero-median ray is thin and close to the postero-external. Posterior ray bifurcate, each branch bifid at the tip (fig. 311). Spicules short, spoon or spatula-like, with on the broad anterior end a lateral knob or disc and in front of the point an angular projection. Gubernaculum of a peculiar canoe or shoe shape in profile. Vulva in the hinder half of the body. Tail with two minute papillæ just in front of tip. Eggs thin shelled; when laid they show eight to thirty-two segments. Parasitic in duodenum, seldom in the stomach of herbivora.

Trichostrongylus instabilis,312 Railliet, 1893.

Syn.: Strongylus instabilis, Railliet, 1893; Strongylus subtilis, Looss, 1895.

Male 4 to 5·5 mm. long, 0·08 mm. thick in front of bursa. Spicule 0·135 to 0·145 mm. long, accessory piece (gubernaculum) 0·07 mm. thick. Antero-external ray usually thickest of all, occasionally only as thick as the antero-median; postero-median far more slender than the antero-external and antero-median and nearer to the postero-external than to the antero-median. Female 5 to 6 mm. long, vulva 1·05 to 1·2 mm. distant from the tip of the tail, placed longitudinally, 50 µ to 55 µ long, always shorter than the unpaired portion of the canal formed by the union of the two ovejectors; anus 0·055 to 0·07 mm. distant from tip of the tail; ova 73 µ to 80 µ by 40 µ to 43 µ.

This species lives in the duodenum, exceptionally also in the stomach of Ovis aries, O. laticauda, Antilope dorcas, Camelus dromedarius (Egypt), Cynocephalus hamadryas (North Africa), sheep and goats (France), and has been found by Looss in bodies of fellaheen at Alexandria and in the stomach of a Japanese female by Ijima.

Trichostrongylus probolurus, Railliet, 1896.

Syn.: Strongylus probolurus, Railliet, 1896.

Male 4·5 to 5·5 mm. long, in front of bursa 0·08 mm. thick; spicule 0·126 to 0·134 mm. long, gubernaculum 0·075 to 0·08 mm. long. Bursa: latero-anterior rib thickest; antero-external thicker than antero-median, postero-median and postero-external very short and close together. Female 4·5 to 6 mm. long, vulval opening 1·08 to 1·25 mm. from tip of tail, placed longitudinally, and slightly curved, 76 µ long, always longer than the unpaired portion of the ovejector; anus 0·040 to 0·05 mm. distant from tip of tail. Posterior end thick, point of tail short. Ova 76 µ to 80 µ by 43 µ to 46 µ.

Male 4 to 5·5 mm. long, in front of bursa 0·085 mm. thick. Bursa larger than in the other two species, antero-external rib thickest, antero-anterior and postero-median equally thick, straight. Spicule 0·16 to 0·17 mm. long, gubernaculum 0·085 to 0·095 mm. long. Female 5 to 6·5 mm. long, vulval opening 1·15 to 1·25 mm. distant from tip of tail, crescent shaped, oblique to body axis, and around it irregular thickenings. Ova 84 µ to 90 µ by 46 µ to 50 µ.

In duodenum of Ovis aries, O. laticauda, occasionally in Camelus dromedarius and in man (Egypt).

Male 20 mm. long by 400 µ thick (maximum). Asymmetrical lobe of bursa 150 µ by 125 µ attached to left lateral lobe. Posterior ray bifurcate; each branch bifid. Stem of ray less than twice as long as its branches. Spicules 300 µ to 500 µ with knobbed tips, and the left spicule with a barb 20 µ from the tip, right spicule with a barb 40 µ from tip. Gubernaculum 200 µ by 25 µ to 35 µ, fusiform with thickened edges.

Pathology.—Produces anæmia, emaciation, dropsy in sheep; and in the human case the symptoms were mistaken for those of ancylostomiasis.

Life-history.—Rhabditic embryos easily hatch in water, then moult several times, becoming eventually “filariform” larvæ enclosed in the moulted skin. These crawl up blades of grass and are swallowed by sheep, etc.

Genus. Nematodirus, Ransom, 1907, emend. Railliet, 1912.

Head over 50 µ in diameter. Cuticle may be slightly inflated and often transversely striated. Cuticle with eighteen distinct longitudinal ridges. Cervical papillæ absent (?). Posterior lobe of bursa reduced to short lobules each with a dorsal ray. Antero-anterior + latero-anterior (= anterior double) rays close together, parallel; antero-external ray diverges widely from antero- and postero-median, which are close together and parallel. Postero-external ray slender. Spicules more than 0·5 mm. long, at most one-twelfth of body, united by a membrane throughout their length or only distally. Gubernaculum absent. Vulva behind middle of body. Eggs ellipsoidal, shell rather thick.

Habitat.—Duodenum of ruminants.

Sub-genus. Mecistocirrus, Railliet, 1912.

Head slightly inflated, with transverse striations. Skin with eighteen longitudinal ridges, but little apparent; cervical papillæ distinct. Bursa bilobed; median ray double (= postero-median + antero-median); very large antero-external at the edge, close to the anterior. Spicules very long, slender, one-sixth length of body (3·5 mm.); tail pointed. Vulva immediately in front of anus.

Habitat.—Stomach of ruminants.

Mecistocirrus fordi, Daniels, 1908.

Syn.: Strongylus fordi, Daniels, 1908; Strongylus gibsoni, Stephens, 1909; Nematodirus fordi, Leiper, 1911.

Male 21 mm. long by 0·4 mm. thick. Cervical papillæ 0·45 mm. behind the head. Spicules about 7 mm. long, i.e., one-third of the body length. At the level of the postero-external rays of the bursa, the bursa has a projecting lobule.

Group. Œsophagostomeæ, Railliet and Henry, 1909.

Bursa with anterior and median ray cleft (not double), postero- and postero-external arising from a common trunk, posterior bifurcated, each limb bidigitate.

Contains at present four genera: (1) Ternidens, (2) Chabertia, (3) Œsophagostomum, (4) Agriostomum.

Genus. Ternidens, Railliet, 1909.

Buccal capsule sub-globular, opening obliquely in the dorsal surface, and having at the bottom three complex teeth resembling those of Triodontophorus.313 Two crowns of leaflets; peristomic collar moderate, edge of bursa slightly toothed.

Type.—T. deminutus, Railliet and Henry.

Ternidens deminutus, Raill. and Henry, 1905.

Syn.: Triodontophorus deminutus, Raill. and Henry, 1905.

Body relatively thick. Cervical papillæ 0·5 mm. behind the head. Buccal capsule 40 µ deep. Teeth 40 µ long.

Female 12 to 16 mm. long by 650 µ to 730 µ thick. Œsophagus 860 µ long. Vulva forms a distinct projection 480 µ from tip of tail. Anus 240 µ to 270 µ from tip. Eggs 60 µ to 80 µ by 40 µ.

Habitat.—Large intestine of a negro (Comoro Islands) and in the natives of Nyasaland and Portuguese East Africa. Also in large intestine of Macacus sinensis and Macacus cynomolgus.

Genus. Œsophagostomum, Molin, 1861.

No teeth. Cuticle around the mouth dilated to form a narrow cuticular “peristomic collar.” Separated by a constriction from this is a much more extensive inflation, the “cephalic vesicle,” bounded abruptly behind on the ventral side by a transverse groove, the “ventral cleft,” which is always present even in absence of the vesicle. Buccal cavity of slight depth with a short dorsal tunnel. Internal margin of the mouth armed with chitinous leaflets (“external crown”); internal border of the buccal capsule armed with short tongue-like leaflets (internal crown). Lateral membranous wings may extend backwards from the ventral cleft. Cervical papillæ present. Bursa with two lateral lobes united by a smaller median lobe. Spicules over 5 mm. long, slender; gubernaculum inconspicuous. Vulva in front of anus. Adults usually in large intestine of ruminants, suidæ, tapirs, edentates and apes. Larvæ sometimes in nodules in intestinal wall.

Œsophagostomum brumpti, Railliet and Henry, 1905.

Female immature, 8·5 to 10·2 mm. long, 0·295 to 0·325 mm. thick. Cuticle transversely striated. The cephalic vesicle immediately behind the vestibulum oris, embracing the anterior two-fifths of the œsophagus, extending ventrally, however, towards its posterior end. Vestibulum oris formed by a cuticular band provided with a crown of twelve apical leaflets directed forward and inwards; six cephalic papillæ (two lateral, four submedian); buccal capsule in front of cervical swelling not delineated circularly behind, but provided with three wide incisions (one dorsal, two sub-ventral). Œsophagus, 0·470 to 0·500 mm. long, two cervical papillæ at five-eighths of its length. Vulva 0·350 to 0·475 mm., anus 0·170 to 0·200 mm., before tip of tail.

Habitat.—Found by Brumpt in tumours of the cæcum and colon of a native of the River Omo (Lake Rudolph), East Africa. Immature forms only were present. Adults have been found in similar tumours in monkeys.

Pathology.—They occur in hæmorrhagic cysts in the submucosa or muscularis mucosæ of the gut wall. The cysts project internally and externally, and contain immature adults, which eventually escape into the lumen of the gut.

Body thick, pointed only at the ends. Buccal capsule much reduced. External crown of thirty-eight leaflets (the “crown” nearest the centre of fig. 319, 5). Male 17 to 22 mm. long by 750 µ thick. Spicule 1·380 to 1·475 mm., slightly curved at the tip. Female, immature, 16 to 20 mm. long by 900 µ thick, tail ending in a little conical appendage. Anus 230 µ, vulva 500 µ to 525 µ from tip. Ovejectors close together. Uteri very short in form of oblong pouch.

Œs. stephanostomum, Stossich, 1904, in the large intestine of gorilla. Œs. stephanostomum var. dentigera, Raill. and Henry, 1909, in the chimpanzee.

Habitat.—In large and small intestine of man, Brazil.

Pathology.—Nodules occur in the gut wall; 187 were found by Thomas in his, the sole case. The tumours contain each a single worm.

Group. Ancylostomeæ, Railliet and Henry, 1909.

Bursa with anterior ray cleft, median double,314 postero- and postero-external arising from a common trunk, posterior bifurcate, each limb being tridigitate. Vulva in posterior third of body. Uteri divergent.

Contains the following genera: (1) Strongylus,315 (2) Ancylostoma, (3) Uncinaria, (4) Characostomum, etc.

Genus. Ancylostoma, Dubini, 1843, emend. Looss, 1905.

Ventral margin of mouth capsule armed with teeth, the “roots” of which are continued backwards and appear on the external surface of capsule as rib-like thickenings. Terminal third of dorsal ray cleft. Genital tubes very long, with short, closely packed diagonal convolutions.

Ancylostoma duodenale, Dubini, 1843.

On the ventral wall one sees the two pairs of strong teeth, their points being directed somewhat backwards. They are covered by cuticle above and below, but their points are free, piercing the cuticle. The “roots” of these teeth followed backwards appear as two thickenings or ribs on the outside of the capsule wall, so that the outside wall is not smooth—a characteristic of the genus Ancylostoma. In the space between these ribs lies the ventral nerve papilla, and lying against the outside of the outer root the lateral nerve papilla. The nerve papillæ are thus, as it were, concealed by these roots, and not conspicuous as they are in Necator. Following the ventral curve of the capsule on the inside, posteriorly we next find two triangular ventral lancets.316 These stand straight up into the capsule on either side of the longitudinal axis, converging at their summits. So that to sum up, the cutting apparatus is entirely ventral, consisting of two pairs of cutting teeth and a pair of lancets.

Cervical Papillæ.—Two, one on each side behind the head at the level of the excretory pore. They consist of “pulp,” i.e., extensions of the substance of the lateral bands covered by cuticle and supplied with a nerve (fig. 326).

Excretory System and Cervical Glands (2).—The excretory pore lies in the mid line ventrally behind the œsophageal nerve ring (figs. 324 and 326). It opens into the excretory vesicle, a cavity in a large cell with lateral appendages which fuse with the lateral lines, this cell thus forming the “bridge” of the excretory system. Adhering to this (bridge) cell are the spindle-shaped cervical glands (Glc, fig. 324), and branches from the excretory vesicle enter the glands, which are excretory in function; the vesicle also receives branches from the lateral excretory canals (fig. 326) running in the lateral lines or bands. The cervical glands are swollen anteriorly, forming the so-called ampullæ just in front of the bridge. They extend backwards a little beyond the anterior loop of the testis.

The Bursa is closed on all sides with a short median (ventral) lobe, which may be tucked inwards. It is an outgrowth of the inner layer of the skin pushing the outer layer before it, so that it consists of three layers, not four, as it would be if it were a fold. The bursa is twice as broad as long. It is supported by a variety of rays, the arrangement of which is best followed from the figure (fig. 327). The different terminology for these rays as used by various authors should be noted: Ventral = anterior; externo-lateral = antero-external; medio-lateral + postero-lateral or antero-median + postero-median = median (doubled); externo-dorsal = postero-external; dorsal = posterior. All the rays end in tactile papillæ, seven, on each side; the postero-external and antero-external on the outer surface of the bursa, the five others on the inner surface.317 Of the six terminal digitations of the dorsal ray, only the external two contain tactile papillæ.

In the male there are prebursal papillæ and minute caudal papillæ in the female.

In the female the inner layer of the cuticle projects at the posterior end as a sharp spike, 20 µ long, which may sometimes be broken off.

Testis.—The blind end begins a little behind the beginning of the cement gland. The transverse coils occupy the middle third of the body. About the middle of the body it passes into the spindle-shaped seminal vesicle, which, with the spicular canal and rectum, opens into the cloaca. An anterior longitudinal coil pushing in between the cervical glands is characteristic of Ancylostoma. The cement gland surrounds the ejaculatory duct for practically its whole course, and it occupies nearly the posterior half of the body and secretes a brown or black cement. The spermatozoa are curved rods about 2 µ long.

Spicules are 2 mm. long, ending in a fine point. They are moved by exsertor and retractor muscles. At first they lie free in the body cavity; next in a groove in the dorsal wall of the cloaca; then in an isolated canal, and finally in two canals. Anteriorly each has two longitudinal crests on its inner surface. These meet the corresponding crests of the other spicule, and so form a canal along which the sperm passes into the female. The gubernaculum is a thickening of the dorsal wall of the cloaca. It is not a free piece, but is moved by various muscles.

Development.—The eggs are oval with broadly rounded poles, 56 µ to 61 µ by 34 µ to 38 µ. In fresh fæces they contain four granular nucleated segmentation masses of the ovum (fig. 329) separated by a clear space from the shell.

Embryos which are ready to hatch have their bodies almost free from granules; others, though apparently mature, that have granules will not hatch.318

Larva.—Stage I: Average length, 25 mm. Maximum thickness in œsophageal region, 17 µ. Head end fairly blunt, from behind the anus (the tail) tapering in an uniform manner. Buccal cavity is characteristic, 10 µ to 12 µ by 1 µ to 8 µ, longer and narrower than the corresponding larvæ of Strongyloides stercoralis. Œsophagus “rhabditic” in character, i.e., it has three sections, but they are not so clearly marked off as in larvæ of the genus Rhabditis. The posterior bulb has a Y-shaped valve, the function of which, according to Looss, is to prevent regurgitation of food. The granules of the gut serve as a reserve of food, and are used up if the larvæ are starved. The genital rudiment consists of two cells half-way between the end of the œsophagus and the anus in the mid-ventral line. The larva lives on fæcal matter and grows to about 0·4 mm., then moult319 I takes place in two days or more, the skin being ruptured by the activity of the larva.

Stage II: The larva is now in this stage, which does not differ much from the previous one. It grows to 0·5 mm. The mouth opening closes. The œsophagus elongates, becoming cylindrical or “filariform”; a new skin is formed underneath the old one, and in about a week moult II takes place.

Stage III: The mature larva remains enclosed in the old skin. Its movements are now much more active and of a boring character. Length is now 0·6 mm. This mature stage has been erroneously called the encysted larva, because there is no cyst secreted from its surface by the larva, but it is simply the old skin, which is not cast off, but is retained for purposes of protection, as the larva is free living, but casts it as soon as it assumes parasitic life again. From the egg to this mature stage is thus six to ten days.

Moisture: Eggs and larvæ do not live long under water, because they suffocate or starve, but mature larvæ will live for months (six to twelve) in water; they require no food—in fact, can take none in—but live on their reserve granules, and in course of time become as clear as glass.

Thigmotropism: The mature larvæ, after casting their skin, will penetrate pith, climb up stems, stalks, etc., and creep into any pore.

It is important to recognize that this third stage of the mature larva is the only infective one.

Mode of Entry into the Body.—Infection is effected through the mouth (Leichtenstern and others), and also through the skin, as was first discovered by Looss and afterwards confirmed from the most diverse quarters, partly in the case of Ancylostoma duodenale, partly in that of A. caninum in dog, man, and monkey. The larvæ that gain access to the intestine partly through contaminated food, or through unwashed hands, or under some circumstances through water, first throw off their “sheath”—that is, they complete moult II. Moult III takes place four to five days after they have reached the gut, and they now have a mouth capsule supplied with four small teeth arranged crosswise, enabling them to fasten on to the intestinal epithelium, upon which they feed. On this food the worms grow in four to six days to 3 to 5 mm. in length, and now moult IV. takes place, thus attaining their definite shape and distinctive character. About eight days later the sexual organs commence to function; at this time the first copulation should be taking place—it will later be frequently repeated—and a few days later the first ova are laid, first in less and later in larger numbers, so that they appear in the fæces about four to five weeks after the infection.320

Infection by the Skin.—Mature larvæ, which are placed on the skin of man or suitable animals, cast their “sheath” and bore their way through delicate fissures either horizontal in the superficial scales of the epidermis, or through vertical fissures into hair follicles where these exist, and then they invade the cutis. Now according as they migrate further into the lymphatic vessels or the small vesicles, the final path to the gut differs to some extent. The blood path leads to the right heart, and from there into the lungs; here the larvæ leave the blood stream and enter the air passages, over the mucosa of which they travel further headwards, through the bronchi into the trachea and larynx, and from hence through the œsophagus to the stomach; in some cases also they are swallowed. The lymphatic path leads finally also into the blood stream, but the lymphatic glands must first be passed, and in these many larvæ are retained and perish. In the cutaneous infection seven to ten weeks elapse till the time of appearance of the first ova in the fæces.