5IO MICRO-ORGANISMS AND DISEASE [chap. 



while not one amongst them is able to do more than draw 

 attention to certain morphological appearances in the 

 epithelium which are put forward as denoting the presence 

 of something extraneous to the typical epithelial cells. No 

 one has in regard of cancer ever succeeded in isolating the 

 parasite, as is easily enough done in the psorospermosis of the 

 rabbit ; and, notwithstanding all assertions to the contrary, the 

 evidence amounts only, as I have said, to the description of 

 certain bodies which, after certain methods of staining, can 

 be demonstrated within or between the' epithelial cells in the 

 above human affections. Amongst these bodies, however, 

 none are typical psorosperms. Under these circumstances 

 the critics of those who affirm a parasitic cause of cancer 

 have an easy task ; they can with perfect justification 

 demand, where — if such-and-such indefinite and mysterious 

 bodies do occur in cancerous epithelium — is the proof that 

 they are of a parasitic nature. To this the others can only 

 reply that they are most probably parasites, because they 

 are not typical epithelial cells. But how do you know that 

 they are not part of the cell or nucleus ? again ask their 

 critics. Because they stain differently from epithelial cell 

 substances or epithelial nucleus, answer the upholders of 

 parasitic cause. But surely, retort their critics, you have no 

 right to call those bodies psorosperms merely because you 

 are unable to think of them as derivatives of the substance 

 of the epithelial cells or their nuclei. And so on, and so on. 



I have I think thus given sufficient account of the general 

 nature of a great part of the controversy ; at least it is not 

 necessary for the present to go further into details, as will 

 duly appear later on. 



Before coming to the discussion of the alleged parasites 

 of cancer and of other chronic epithelial diseases in man 

 that I have referred to, it is necessary to have a clear view 



