THE " HABIT OF GROWTH " THEORY 303 



which does not go on to exhaustion and excessive breaking-down 

 of their protoplasm ; provided, also, that the microbes and their 

 products continue in action for a sufficiently long time to set up 

 the habit of growth. It is quite conceivable that such microbes 

 might continue to exist in the tumours they originated, exerting 

 a cumulative effect. The more the cells depart from type the 

 greater the effect of these microbes and their products in pro- 

 ducing a tissue of rapidly proliferative and malignant type. 



This continuance and persistence of microbic action, however, 

 must not, I think, be regarded as essential. The very fact that 

 after all these years, and after the hosts of careful observations, 

 we are still in very grave doubt as to whether any of the bodies 

 seen in tumours are really parasites, the fact that no growths of 

 these bodies have surely been obtained outside the organism, 

 and then upon injection have induced tumour formation, although 

 by no means proof absolute, may be quoted in favour of the view 

 that if microbes originate malignant tumours, they do not 

 continue in the living state. 



I was not a little interested to note that while Sanfelice * was 

 apparently able in his observations to induce the formation of 

 neoplasms in two out of rather a long series of animals, following 

 upon inoculation of these animals with his blastomycete — the 

 Saccharomyces neoformans — when he came to make cultures 

 from the tumours and from the other tissues of the animals 

 possessing these developed tumours he was unable to gain any 

 growths. An observation somewhat to the same effect I have 

 come across recorded by Dr. T. Harris, 2 of Manchester, in a case 

 of cancerous growth of the bladder associated with and evidently 

 secondary to bilharzia disease. Harris calls particular attention 

 to the fact that although there were abundant ova of the bilharzia 

 in the surrounding vesical tissue, the tumour itself stood out 

 completely free from any sign of these parasites. 



It is quite possible, according to this theory, that certain 

 specific forms of microbic life originate certain forms of tumour 

 growth — of cancer and sarcoma, for example ; that, like other 

 pathogenic microbes, these may show a predilection to attack 

 special tissues under special conditions ; and if it be true (for 

 some doubt continues to be thrown upon the matter) that 



1 Sanfelice, Centralbl. f. Bali, xxiv., 1S0S, 8. 166. 

 2 T. Harris, Trans. Path. Soc, London, vol. xxxix. p. 183, 1888. 



