296 MICROBES AND TOXINS 



trypanosome neither in vitro nor in vivo ; others are active in 

 both, for example, tartar-emetic. 



Methylene-blue kills certain spirochaetes in the test-tube in 

 a dilution of i in "6,000,000, but has no action in the body of 

 a mouse even when in 500 tim.es greater concentration. 



Atoxyl does not act in vitro but acts in the living body. 

 There are even substances which in the body stimulate the 

 multiplication of certain parasites ; one must here reckon with 

 the body as a factor as well as the parasite, and the problem 

 of the best drug to use both in the first attack and in relapses 

 is a new one for each species of trypanosomes, and for each 

 species of animal : chemical therapeutics is therefore not 

 likely to become more simple. 



When an animal acquires immunity towards a bacterial 

 infection, there develop, as we have seen, antibodies, as manifested 

 by new properties of the .serum, bactericidal, preventive, and 

 curative. Is it the same in protozoal infections? Do the 

 chemical remedies induce the formation of antibodies ? 



The seruin of animals infected with trypanosomes possesses 

 microbicide and preventive properties, weak it is true, but 

 definite; they appear in the course of chronic or subacute 

 infections. There is reason to believe in the presence of an 

 immune body analogous to those known in antibacterial 

 immunity ; it acts by inducing a phagocytosis of the parasite. 



Strains of protozoa may arise resistant to the serum of 

 animals, infected or provisionally cured, just as with the 

 chemical remedies ; in many cases it is a true variety forma- 

 tion, for the acquired character can be transmitted through 

 several generations (counted by mouse passage). 



The antibodies in animals infected by trypanosomes originate 

 doubtless from trypanosomes destroyed and absorbed. At the 

 same time, the rapid destruction of a great number of the 

 parasites may flood the body of the host with substances which 

 act as poisons — a sort of endotoxins. In a man suffering from 

 sleeping sickness, a disappearance of the trypanosomes under 

 the influence of atoxyl is often followed by an attack of fever 

 (L. Martin). 



