INFECTION AND MALIGNANCY 279 



5. While the cases on record of apparent direct infection 

 from one individual to another are so few as to be explained 

 by the law of chance, and as being but the coincidental occur- 

 rence of the same disease in two associated individuals, and 

 while the experimental inoculation of fresh cancer material 

 from one individual to the other (whether these be of the same 

 or of different species) has almost uniformly failed, nevertheless, 

 in rare cases, this would have appeared to have succeeded ; 

 and, according to Sanfelice, the inoculation of a pure culture of 

 a yeast isolated by him has, in a small proportion of cases, led 

 to the production of definite neoplasms. Two factors are neces- 

 sary for successful experimental inoculation — the virulence of 

 the parasite and the susceptibility of the tissues ; and it may 

 well be that if malignant growths are brought about by parasites 

 of a very low state of virulence, a very special susceptibility 

 or special condition of the tissues is necessary for the inoculation 

 to be successful. To this lack of special susceptibility of the 

 tissues is to be attributed the frequent failure of experimental 

 inoculation, either with cancerous material direct, or with pure 

 cultures grown outside the body. 



These, I take it, are the main arguments in favour of the 

 parasitic origin and infectious nature of malignant growths. 

 Stated thus, they present a very strong prima fade case in favour 

 of the parasitic theory. There is, however, I need scarcely 

 say, another side to the question, and each of the above arguments 

 in turn may be, and has been, strongly assailed. 



(1) Some capable observers still hold that increased longevity 

 is capable of explaining the increase. (2) A fuller study of low- 

 lying and estuarial regions shows that while cancer is very common 

 in some, it is equally uncommon in others. (3) The analogy 

 between the mode of dissemination of tuberculosis, for example, 

 and the development of metastatic cancerous nodules is recognized 

 by all histologists as being thoroughly unsound. (4) Further, 

 it is difficult to refute the careful observations of Fabre-Domergue 

 and of Pianese, 1 that the so-called cancer bodies of varying types 

 described by different observers are so many different forms 

 of degeneration products within the cancer cells. When, by 

 employing special staining methods which afford a differential 

 stain for mucoid, pseudo-mucoid, hyaline, and amyloid material, 

 1 G. Pianese, ZeigUr's Beitrage, xx., 1896. 



