86 THE BACTERICIDAL SUBSTANCES OF THE BLOOD 



large numbers of leukocytes which are mainly of the polynuclear 

 neutrophilic type. These dispose of the remaining organisms by 

 phagocytosis, and the peritoneal cavity finally becomes sterile. 



This means, in other words, that the animal which showed no 

 evidence of a defensive reaction in the first experiment, actually 

 had a very definite mechanism of this kind at its disposal, and the 

 conclusion is, no doubt, justifiable that in the first instance the dis- 

 tribution of the normal bactericidal substances of the serum among 

 the enormous number of bacteria (or its exhaustion by relatively 

 few organisms) was insufficient to bring about any recognizable 

 effect, and its renewed production, if, indeed, this occurred at all, 

 was too small or delayed too long to cause any material retardation 

 of the final outcome. 



The appearance of the second line of defence, viz., the leukocytes, 

 was evidently also delayed too long, if, indeed, we are permitted to 

 speak of a delay at all under such conditions where there is evidence, 

 both experimental and clinical, to show that in infections with over- 

 whelming numbers of organisms the leukocytic mobilization may be 

 arrested almost altogether. 



If we compare the picture illustrated by the second experiment 

 with what we have seen in the corresponding anthrax experiment 

 there is a certain resemblance, for here as there the peritoneal cavity 

 is virtually freed from bacteria soon after the primary invasion; but 

 while in infections with the semiparasites or at least with organisms 

 of the type of the typhoid and cholera bacilli, the organisms remain 

 absent, or become so (unless too large a dose had been chosen) in 

 anthrax there is invariably a second phase which is characterized 

 by the return of the germs and their subsequent multiplication 

 without further hindrance, even when a small dose has been injected. 



Another point of difference also exists which is important, for 

 whereas in the anthrax experiment the primary bactericidal effect 

 was due to an associated phagocytic and aphagocytic activity of 

 the leukocytes (in the presence of serum), the primary destruction 

 of the cholera vibrios was essentially brought about by the normal 

 bacteriolysins of the serum. Whether during the second phase 

 of the cholera experiment, when the leukocytes appear, a leukin 

 action also takes place, seems doubtful. If it occurs it certainly 

 plays a relatively insignificant role. Then, again, while animaliza- 

 tion (encapsulation) of the anthrax bacilli leads to successful resist- 



