INFECTION AND IMMUNITY 163 



The antibody content of the serum, ^wever, is 

 not always the same as that of the blood plasma. 

 Thus Gengou, by collecting the plasma in vaselined 

 tubes, found it often to be almost devoid of bac- 

 tericidal power, while the corresponding serum was 

 capable of destroying large numbers of microor- 

 ganisms. In these cases, it is evident, we cannot 

 regard plasma destruction of bacteria as the impor- 

 tant factor in immunity. Moreover, in the case of 

 bacteria containing considerable quantities of endo- 

 toxin, it is conceivable that plasma destruction of 

 bacteria may even do considerable harm by 

 causing an enormous liberation of endotoxin. This 

 point is perhaps of practical importance as contra- 

 indicating the use of bacteriolytic sera in the 

 curative treatment of certain infections. 



From what has been said it is evident that the 

 exact mechanism of immunity, at least so far as 

 most infections are concerned, is still very obscure. 

 Like most biological phenomena, the deeper we 

 analyze the problem, the more complex and more 

 marvelous it becomes. Enough has, however, been 

 presented to show some of the difficulties to be 

 overcome and the method of attacking the sub- 

 ject. 



Relation of Anaphylaxis to Immunity. We have 

 already discussed the relation of anaphylaxis to 

 infection and may now take up briefly its relation 

 to immunity. We know that the subcutaneous, 



