334 Chapter XI 



and were able to show that a non-venomous snake (Tropidono- 

 tus) will withstand a dose of venom capable of killing from 15 to 

 20 guinea-pigs. Seeking for the cause of this natural immunity, 

 these observers came to the conclusion that it is due to the 

 presence in the blood of toxic substances analogous to those of the 

 venom of the viper. These same substances are found also in the 

 labial glands of the upper jaw of the Tropidonotus and can from 

 thence, according to the view of Phisalix and Bertrand, pass into the 

 blood as an internal secretion. Calmette^ has shown that the blood 

 of snakes, injected in a non- toxic dose, vaccinates certain mammals 

 against snake venom, and Phisalix and Bertrand have even obtained 

 an antitoxic effect by injecting a mixture of snake's blood, heated to 

 58° C, with lethal doses of venom. There is, then, in this example 

 [351] something analogous to what we have described in scorpions, with 

 this difference, however, that the blood of these Arachnids is already 

 antitoxic, to a certain degree, whilst that of snakes only becomes 

 so after it has been modified by heat. 



The classic example of immuuity against a bacterial toxin 

 amongst Birds is that of the fowl, which is highly refractory against 

 the tetanus toxin. In the very earliest researches on this poison 

 injections were made into vertebrates of very different kinds, and a 

 very striking featui'e was the facility with which fowls resist very 

 large quantities of tetanus toxin. However, as is almost always the 

 case, this immunity has been found not to be absolute. By means of 

 enormous doses, injected subcutaneously or into the muscular tissue, 

 tetanus of the most typical kind, ending in death, has been induced in 

 fowls, and in fowls weakened by cold, tetanic intoxication, even with 

 smaller doses, has been set up. By injecting the toxin directly into 

 the brain, according to Roux and Borrel's method, the fowl may be 

 still more easily tetanised. Thus, von Behring^ observed that by 

 injecting one milligramme of the toxin into the brain of a fowl, 

 weighing one kilo, tetanus may infallibly be produced. 



After the brilliant and fruitful discovery of the antitoxic property 

 of the blood, made by von Behring in collaboration with Kitasato, 

 we were justified in concluding that immunity against toxins and, 

 amongst others, natural immunity, might depend on the power of the 

 body fluids to neutralise the toxins. This hypothesis has been formu- 

 lated at various times, but it was for the first time subjected to 



1 " Le venin des serpents," Paris, 1896, p. 40. 



2 " Allgemeine Therapie der Infectionskraukheiten," Berlin u. Wien, 1S99, S. 992. 



