IMMUNITY AND SUSCEPTIBILITY. 141 



The phenomena of phagocytosis as seen in acquired 

 immunity are very interesting. Every one that has 

 studied anthrax infection and examined the blood and 

 juices of the dead animal, is familiar with the fact that 

 the leukocytes never touch the bacteria. If, however, 

 the animal be vaccinated to anthrax, the phagocytes are 

 said to take up the virulent bacilli regularly. 



In the researches of Werigo 1 upon the immunity of 

 the rabbit to symptomatic anthrax it was found that in 

 the normal animal the phagocytosis is irregular, many 

 bacteria being taken up by the leukocytes, but enough 

 allowed to remain to carry on the diseased process. In 

 the vaccinated animal the phagocytosis is prompt and 

 efficient. He thinks that in the process of immunization 

 the leukocytes become so sensitive to the bacterial in- 

 fluences that the least particle of their toxic products 

 is sufficient to attract them to find and destroy the 

 bacteria. 



In infection with vibrio Metschnikovi it has been 

 shown by Metschnikoff that the phagocytes of unpro- 

 tected animals do not take up the bacteria, but that in 

 vaccinated animals the phagocytes are loaded with 

 them. 



It is thus apparent to the reader that according to the 

 degree of immunity the phagocytes are active. Whether 

 or not they are active because the animal is immune and 

 the bacteria harmless for them, or whether the animal is 

 immune because they are hurtful to the bacteria, remains 

 an important question as yet unsolved. 



IV. Germicidal Action of the Blood. — This 

 phenomenon, like that of phagocytosis, is apt to develop 

 in proportion to the degree of immunity attained. It 

 does not always follow, however, for in immunization to 

 the specific toxins of the micro-organismal affections the 

 blood does not become germicidal to the respective 

 germs. The so-called antimicrobic serums character- 

 izing forced immunity have already been discussed in a 



1 Archiv de Med. experimentalle et d' Anatotnie pathologique, t. x., p. 725. 



