EFFECTS OF PROTOZOAN PARASITES UPON THEIR HOSTS 203 



Here, then, is a change which, as Siedlecki points out, recalls the con- 

 dition which Hertwig ('04) shows is characteristic of degenerating 

 cells, the simplification of the cell type from a more complex "organo- 

 type" into a simple " cytotype," or a return to the embryonic condition. 



The specific efi'ect of the young caryotropha on the infected cell 

 consists not only in the enlargement of that cell, but of a definite feed- 

 ing mechanism by which the parasite is supplied with food. That 

 the nucleus is the seat of constructive metabolic changes is well assured 

 at the present day, and the conditions in these parasites suggest the 

 peculiar relation which Shibata ('02) has described in the intracel- 

 lular mycorhiza, where a mycelium thread is grown straight toward 

 the nourishing cell nucleus of the host, causing marked hypertrophy 

 on the part of the cell. In caryotropha the nucleus of the host cell is 

 pushed to one side and the parasite assumes such a form that the 

 nucleus lies in a small bay (Fig. 84). In the cytoplasm of the cell an 

 intracellular canal is then formed which runs from the host nucleus to 

 the nucleus of the parasite, and Siedlecki holds that the food of the 

 parasite is all elaborated by the nucleus of the host cell, while the other 

 spermatogonia form a protective epithelial sheath around it. When 

 the parasite is full grown the cell is destroyed and the bundle 

 degenerates. 



Not only hypertrophy of the cell, but of the nucleus as well, may be 

 caused by the presence of protozoan parasites. Doflein ('07) has 

 shown that the nucleus of Ameha vespertUio becomes greatly enlarged 

 through the action of intranuclear parasites, and similar enlargement 

 is characteristic of the skin cells in smallpox lesions. Lfeger and 

 Duboscq ('04) noted that gregarines may cause the formation of 

 multinucleated cells, while in some forms (Styhrhynchiis oblongatus 

 and St. longicollis) the epimerite penetrates the cell and rests in 

 the vicinity of the host nucleus. In these cases the French observers 

 state that the parasites attached to the epithelial cells prevent the 

 normal nourishment of the latter and also prevent the cells from 

 secreting properly, so that they do not develop but remain of embryonic 

 type, and may even divide. Where the parasites are abundant in an 

 organ the destruction of cells is too rapid for regenerative processes to 

 keep up. Thus, Schaudinn ('02) has shown that Cyclospora caryolytica 

 may be so abundant as to cause acute enteritis and death of the mole, 

 its host, within a few days. Here the effects are purely mechanical, 

 and in this category belong the great majority of protozoan parasites, 

 especially those forms which are intracellular during part or the whole 

 of their life. Liver cells, muscle cells, even heart cells, may all be 

 destroyed by some form or other of protozoan parasite, usually a 

 sporozoan, and these cytozoic forms rarely confer immunity on the 

 host organism. 



