20 Chapter I 



cultures of the diphtheria and the tetanus bacillus grown in broth 

 and deprived of the bacilli by filtration as large as those of ordinary 

 broth alone in which no bacilli have been cultivated. Gengou 

 argues from this that the Paramaecia possess a natural and absolute 

 immunity against these two toxins. When we take into consideration 

 the fact that these poisons act but feebly at ordinary temperatures 

 and are often innocuous to " cold-blooded " animals we may perhaps 

 be tempted to attribute the immunity of the Infusoria to the tem- 

 perature that was maintained in the incubator whilst Gengou's 

 experiments were being carried on. Led by this train of thought 

 Mme MetchnikoiF tried the action of the blood-serum of eels, which 

 is very toxic, not only for warm-blooded Vertebrates but also for cold- 

 blooded Vertebrates and the In vertebrates, on the Paramaecia,axid this 

 at a low or medium temperature. This eel's serum, however, exerted 

 no greater toxic action than did the blood-serum of other animals. 



The microbial toxins are innocuous not only to the ciliated 

 Infusoria but also to many other unicellular organisms. It is now 

 well recognised that these toxins, exposed to the air, are soon 

 inhabited by quite a rich flora of micro-organisms, amongst which 

 Bacteria and Yeasts predominate. I have been able to prove 1 that 

 these organisms are not only unaffected in their normal life by the 

 presence of the toxins of diphtheria or tetanus but that they rapidly 

 bring about the more or less complete destruction of these poisons. 

 Gengou, also, observed that yeasts thrive luxuriantly in these bacterial 

 toxins. The rapid increase of micro-organisms and the destruction 

 of these poisons take place at temperatures varying from 15 to 37 C. 



Whilst the lower organisms are refractory to bacterial toxins 

 which in quite small doses are capable of killing man and the 

 higher animals, many micro-organisms manifest a special sensitive- 

 ness to certain fluids of animal origin. In a succeeding chapter 

 we shall treat at greater length of this microbicidal property of 

 the humours. Here it is merely necessary to indicate certain facts 

 concerning this property, regarding them solely from the point of 

 [23] view of the immunity of the lower organisms. The most striking 

 example of the bactericidal power of an animal fluid is certainly 

 that afforded in the action of the blood-serum of the rat on the 

 anthrax bacillus. This fact, discovered in 1888 by von Behring 2 , led 



1 Ann. de VInst. Pasteur, Paris, 1897, t. xi, p. 801. 



2 "Ueber die Ursache der Immunitat von Ratten gegen Milzbrand," in the 

 Centralbl.f. klin. Med. t Bonn, 1888, no. 38. 



