THE PROBLEMS OF THERAPEUTICS 179 



of our own digestion are poisonous and if the albumoses and pep- 

 tones formed by the digestion of a beef-steak in the stomach were 

 injected directly into a man's veins they would kill him, whereas, 

 when changed by the cells of the intestine and liver in the process 

 of absorption, they nourish and strengthen him. 



The complexity of toxins and antitoxins is easily understood 

 when we consider that they are probably all formed by the split- 

 ting- up of albuminous molecules and thus vary enormously just as 

 the splinters of a broken glass vary in size, shape, and in power 

 to puncture or cut. 



In my address at Moscow, in 1897, I ventured to formulate the 

 idea that immunity, natural or acquired, is nothing more than 

 an extension to the cells of the tissues generally of a power which 

 is constantly exercised during digestion by those of the intestine 

 and liver. When microbes were just beginning to be recognized 

 as the cause of infective disease, too much importance was attached 

 to the mechanical effects which they might produce in the blood- 

 vessels and tissues. As their mode of action became better known, 

 this view was to a great extent given up, but though the small 

 vegetable microbes, bacilli and cocci, have little injurious mechanical 

 action, this is not the case with some minute organisms belonging 

 to the animal kingdom, and such organisms of late years have be- 

 come more and more recognized as causes of diseases. In elephant- 

 iasis the lymph channels become blocked by the ova of a small 

 worm which inhabits the blood and thus the enormous swelling 

 characteristic of the disease is produced. Within the last few years 

 that dreadful scourge of tropical countries, malaria, has been dis- 

 covered to be due to an animal parasite, and Manson and Ross 

 have shown that the source of infection is the mosquito. By de- 

 stroying mosquitoes or preventing their multiplication the dis- 

 ease can be to a great extent prevented, but we are still dependent 

 upon bark, quinine, and arsenic as remedies to destroy the para- 

 site and cure the disease. These are not invariably successful and 

 we are still in want of medicines which shall infallibly destroy the 

 parasite. The same is the case with other maladies where the in- 

 fective microbe is of animal origin, as in sleeping-sickness, which is 

 now attributed to a minute worm in the blood, or of vegetable origin 

 as in ulcerative endocarditis, or of uncertain origin as in yellow fever. 



But all these diseases excite much less attention than that 

 which is perhaps more dreaded than any other in temperate 

 climates, namely, cancer. We do not as yet know the pathology of 

 this disease. It has been shown that in it the cells of the affected 

 part multiply and grow in a different manner from that of ordin- 

 ary tissues. They assume a reproductive type and grow inde- 

 pendently of the tissues of the body in which they are situated. 



