144 LEO LOEB. 



segments of scorpions. The scorpions possess, as Metschnikoff 

 describes, in their blood an antitoxin against scorpion venom, 

 which is very poisonous for other insects and to vertebrates. 

 Certain desert animals are frequently exposed to the bite of scor- 

 pions, and in accordance with this fact, it has been recently found 

 that such animals are not susceptible to this poison, although 

 other animals nearly related to the desert animals, but not living 

 in localities where they are exposed to bites of scorpions, are 

 easily poisoned. Whether the blood of these animals has any 

 antitoxic action, does not yet seem to have been determined. 



For a long time an explanation had been sought for the fact 

 that the mucous membrane is not digested by the pepsin and 

 hydrochloric acid, which are secreted by the cells of the mucous 

 membrane. Recently Weinland has shown that the cells of the 

 mucous membrane of the stomach contain a substance able to 

 neutralize the action of the digestive ferment, an antipepsin. 

 Although it is not certain or perhaps even unlikely that the pres- 

 ence of this substance is sufficient to account in itself for the 

 power of resistance shown by the cells of the mucous membrane, 

 yet it represents in all probability at least one important contrib- 

 uting factor and is therefore a cellular adaptation, without which 

 life would be impossible. l 



In the course of the study of the action of bacteria and their 

 toxins on the animal organism, it has been found that injection 

 of bacteria into the body of an animal may cause in the serum of 

 the injected animal the appearance of substances, which produce 

 an agglutination or even a solution of the bacteria (agglutinins, 

 bacteriolysins). Injections of bacterial toxins may produce the 

 appearance of antitoxin in the serum. Later it was found that 

 this response of the animal organism was not limited to bacteria 

 and their products but was also present in the case of injections 

 of animal and plant cells in general and even of ferments and albu- 

 minous substances. The substances which after a certain period 

 are to be found in the blood serum have all this in common that 

 in some way they antagonize the organisms or substances, which 

 had been injected and which had caused the appearance of the 

 reactive substances. The way in which this antagonizing effect 

 does take place is different in different cases. 



1 Metrclinikoff, " L'immunite," Paris, 1901. Chapter XI. 



