XIX] PROTOZOA CAUSING DISEASE 509 



slightest difficulty in recognising these psorosperms and in 

 differentiating them from the epithelial cells. This disease 

 in the fowl is, like the psorospermosis of the liver in the 

 rabbit, essentially' a chronic hypertrophy of the epitheHum 

 caused by the process of growth and multiplication of the 

 psorosperm parasite. 



(c.) Cancer parasites. — There are recognised in the human 

 subject a number of chronic diseases which consist essen- 

 tially in a chronic hypertrophy, with ultimate destruction, 

 of the epithelium 6f the skin, and of various mucous 

 membranes. The principal diseases known as such are : 

 Barrier's disease, molluscum contaglosum, Paget's disease 

 of the nipple of the breast, and last, but not least, various 

 forms of epithelioma and cancer of the skin, mucous 

 membranes, &c. The number of observers who have 

 searched for and found in these various chronic epithelial 

 disorders parasite-like bodies comparable to psorosperms is 

 legion ; but it is equalled, if not surpassed, by the number 

 of other observers, who, though they have searched for these 

 alleged psorosperms in these diseases with equal care and 

 perseverance, have utterly failed to identify them.i While, 

 however, it is one of the simplest and easiest things to 

 demonstrate, by a microscopic examination of the above- 

 mentioned nodular disease of the rabbit, not only the 

 existence of the psorosperms but their relation also to the 

 hypertrophy of the epithelium, it is quite another affair to 

 obtain anything like clear evidence of similar conditions in 

 the above-named human diseases. In the first place, 

 amongst the number of observers who affirm that they have 

 discovered psorosperms in epithelioma of the human subject 

 there are scarcely two who describe the same parasite ; 



^ An excellent summary of all these researches is given by Stroebe in 

 the Ccntralblait jitr Allg. Pathol., &c,, 1894, Nos. i, 2, and 3. 



