IMMUNITY 207 



bleeding the plasma contains no complement, but every 

 minute afterwards injured leucocytes pour into it little by 

 little the active substance. 



Antibodies and Immunity. — There are innumerable 

 facts preventing us from regarding as a law any correspondence 

 between the quantity of antibodies in the serum and the 

 degree of immunity of the animal : this is a definite proof that 

 there is something else besides the humoral properties and that 

 the preponderating part is played by the cell elements. 



The serum of guinea-pigs inoculated against anthrax was 

 found by Behring and Wernicke to be incapable of protecting 

 fresh guinea-pigs from a fatal infection. Pfeiffer immunised 

 guinea-pigs against the bacterium which he regards as the cause 

 of influenza in man, but these immunized animals did not 

 produce a protective serum. 



In protozoal diseases such as malaria, there seems to be 

 immunity in certain cases, but no one has ever demonstrated 

 a protective property in the serum. To take an example 

 among the invertebrates, the larvae of the rhinoceros beetle 

 (Oryctes nasicornis) are immune to anthrax and in them the 

 phagocytic incorporation of injected anthrax bacilli can be 

 very well seen ; yet the blood fluid of these larvae forms a 

 culture medium equally favourable to the anthrax bacillus, to 

 which they are immune, as to the cholera vibrio which produces 

 in them a fatal infection. 



Again, the dog is extremely resistant to anthrax, yet the 

 anthrax bacillus grows very well in dog-serum ; all these are 

 examples of immunity in which the bactericidal power does 

 not play a part. It has been known since the experiments of 

 Behring that rat's serum possesses a remarkable destructive 

 power towards the anthrax bacillus ; now the rat is not 

 immune to anthrax, and the degree of immunity which it does 

 possess is due to the phagocytes. The bactericidal substance 

 exists in the leucocytes, but not in the circulating plasma, nor 

 in plasma carefully prepared by Gengou's method. It exists 

 in the serum, but only because it has been discharged into 

 this by the leucocytes. The rat is extremely susceptible to 



