82 THE BACTERICIDAL SUBSTANCES OF THE BLOOD 



This, however, would be entirely erroneous, for on injecting another 

 guinea-pig with a much smaller dose, e. g., one-half the minimal 

 infecting dose, which after all represents an enormous number of bac- 

 teria, the findings will be altogether different. If specimens of the 

 peritoneal contents are removed at various intervals after the injection, 

 it will be observed at a very early period that active bacteriolysis 

 is already going on which may indeed be so extensive that after one 

 hour the peritoneal cavity may have become microscopically free of 

 organisms. But even if this does not result, the destruction of 

 bacteria is in any event very considerable, and becomes complete 

 through the introduction of a new factor, viz., the appearance of 

 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 evi- 

 dence of a defensive reaction in the first experiment, actually had a 

 very definite mechanism of this kind at its disposal, and the conclu- 

 sion is, no doubt, justifiable that in the first instance the distribution 

 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 defense, 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. 



