These belong to the class of Sporozoa, or unicellular animals with a smooth cuticle. They have little power of movement. These parasites are common in the lower animals, constituting the condition of Coccidiosis or Psorospermosis, chiefly of the liver and intestine.
Coccidiosis is very frequent in the liver in rabbits, both wild and tame. It appears in the form of whitish nodules, often in considerable numbers, which may attain to the size of a hazel-nut. As a large proportion of rabbits is affected, and as it is especially prevalent in the young, the disease is obviously not a very serious one. The white nodules when incised yield a yellow-coloured debris in which innumerable oval bodies are present, the coccidium oviforme, which closely resemble the ova of parasitic entozoa. Closer examination shows that the lesions in the liver are related to the bile ducts, and that there is a new-formation of tissue such as to form a cyst with papillomatous projections from its wall. (See Figs. 162 and 163.) The parasite appears first in the epithelial cells in the form of a small granular body, which grows at first in the substance of the epithelium, distending it as shown in Fig. 163. The parasite finally becomes free and acquires its thick cuticle. These facts are of importance as showing that the presence of this parasite in the epitnelium produces new-formation not only of the epithelium, but of the connective tissue, so as to produce a cystic lesion of definite structure. Coccidiosis also occurs in the intestine of some animals. Nocard has described a case in the sheep in which many small tumours in the mucous membrane of the intestine had a structure comparable with that of the coccidial lesions in the liver.
Few cases of a similar nature have been observed in man, but Gubler has related a case in which the liver was the seat of twenty tumours of cancerous appearance, mostly about the size of chestnuts, but one of very large dimensions. The patient died from peritonitis. The tumours were found encap-suled, and contained internally a creamy fluid which presented countless egg-like bodies having the characters of coccidia. A few additional cases have been observed, but not with such pronounced lesions.
Meischer's or Rainey's tubes are elongated granular bodies found in the muscular substance of some animals, swine, cattle, sheep, and mice. They are supposed to be parasitic protozoa, but their nature is very obscure. Although found in many different animals, sometimes in large numbers, they have not been observed in man.
Fig. 162. - Coccidiosis. Liver of rabbit. Dilated bile-ducts with papillomatous ingrowths from wall.
Fig. 163. - Coccidiosis. Liver of rabbit. From same case as Fig. 162. Numerous granular bodies occupy the epithelial cells. Several parasites which have acquired a thick cuticle are seen lying free.
Molluscum contagiosum, which from its anatomical characters is also called Epithelioma contagiosum, presents conditions strongly suggestive of coccidia and somewhat resembling the phenomena of coccidiosis. The disease, which is contagious, consists, as shown in Fig. 164, of new-formed epithelial structures continuous with the epidermis. It is a proper epithelial tumour, the little nodules sometimes growing to a diameter of almost half an inch. The more central cells are occupied by bodies which in the earlier or outer zones are in the form of small granular structures, with difficulty distinguishable from the protoplasm of the cells. These bodies grow and push the nucleus aside. Finally they assume a capsule and are converted into oval glancing bodies closely resembling coccidia. These are usually called molluscum bodies. If they be really parasites, then we have here again a tumour-like tissue produced by protozoa. It is to be noted here also that the peculiar bodies are closely associated with the epithelial cells, and that they grow in their protoplasm till they reach a state of maturity.
Fig. 164. - Molluscum contagiosum, section on the flat. The new-formed epidermis forms the bulk of the tumour; the central part is occupied by the molluscum bodies, x 12.
Other diseases of the skin have been found associated with bodies believed to be coccidia or psorosperms. Amongst these is Paget's disease of the nipple. The disease is an inflammatory condition of the skin having the usual anatomical features. It has been pointed out by Darier and Wickham that the epithelial cells in this disease contain bodies having the characters of coccidia. It is of importance to note that the disease in question is not infrequently followed by cancer of the mamma, and that the parasites are also found in the epithelial cells of the cancer.
This subject becomes of extreme importance from the fact that similar bodies have been found in the epithelial cells in cancer, and more recently in the cells of sarcomas. This subject has been already dealt with.