THE DEFENSES OF THE BODY 275 



blood-serum from an immune animal, almost instantly the 

 peculiar disintegration of the bacteria that was observed in 

 the peritoneum of the immune animal was to be seen. As 

 we shall learn presently this observation is of the utmost 

 importance and its- bearing upon the course of certain sub- 

 sequent events will soon be manifest. 



The significant features of Pfeiffer's observation are that 

 while the blood serum of an immune animal is capable of 

 conferring immunity upon a susceptible animal, yet, in a 

 test-tube it exhibits none of the bacteriolytic activity con- 

 stantly to be noted in the body of the immune animal; on 

 the other hand if a small quantity of it be injected into 

 the peritoneal cavity of a norrnal, susceptible animal, the 

 phenomenon of bacteriolysis, hitherto absent, at once makes 

 itself manifest. Clearly the serum requires the cooperation 

 of something within the body of the living animal to bring 

 about the disintegration of bacteria. The phenomenon must 

 therefore be the result of a composite function. 



Though Nuttall's work materially lessened the number 

 of adherents to the phagocytic doctrine of Metchnikoff 

 there was still a group of active workers who retained their 

 belief in the fundamental soundness of the idea. Metch- 

 nikoff himself never swerved. Without entering into a 

 discussion of the many instructive investigations upon the 

 questions of phagocytosis it will suffice for our purposes to 

 state briefly their culmination. We now know, through 

 the studies notably of Bail and of Kikuchi that on the one 

 hand phagocytosis may be inhibited, and by the demon- 

 strations of Wright and Douglass, in particular, that, on 

 the other, it may be accentuated. Bail, believing the real 

 defenses of the body to be cellular, attributes the failure 

 of the cells to protect from infection to an inhibition of 



