514 MICRO-ORGANISMS AND DISEASE [chap. 



of the so-called " cancer parasites " in epithelium experi- 

 mentally inflamed, but not of the nature of cancer. 



From the various considerations I have adduced, it must 

 be evident that a number of assertions as to the parasitic 

 nature, in cancer, of various bodies in the substance of the 

 epithelial cells, of nuclear-like bodies between the epithelial 

 cells, of encysted nucleated bodies, of hyaline nucleated 

 cells, of multi-nucleated cells within epithelial cells, and of 

 stained particles within the epithelial nuclei, take no ac- 

 count of the presence of similar bodies and of similar change 

 in epithelium that is not cancerous ; and until such com- 

 parative study of the epithelium in health and in disease 

 has been undertaken statements to the above effect cannot 

 claim that value which their authors attribute to them. 



But I have not completely exhausted the list of difficulties 

 which beset a theory of parasitic cause for cancer. Not 

 least among those that remain is the circumstance that few 

 observers describe the same kind of parasite. One might 

 almost say that there seem to be as many kinds of cancer 

 parasites as there are writers thereon ; and, further, that the 

 morphological characters of most of these alleged parasites 

 do not conform with the characters of any of the known 

 psorosperm species. 



An exception is however to be made in the case of 

 L. Pfeiffer. His numerous researches ^ testify not only to 

 his thorough and extensive knowledge of the subject of 

 undoubted parasitism of sporidia in the animal kingdom, but 

 also in a very high degree to his systematic investigations of 

 the characters and occurrence of these and similar bodies. 

 Whatever, therefore, he has to say on this subject should 



1 Die Protozoen ah Krankheitserreger, Jena, 1890 ; Untersuchunoen 

 liber den Krcbs, Jena, 1893 J """i " ^^^ Parasitismus des Epithelcar- 

 cinoms," Centralblatt f. Bait, und Parasilenk., vol. xiv., page 118, 



