25O OBJECTIONS TO THE THEORY 



position was simple and logical. He pointed out that in mild 

 and non-fatal infections phagocytosis usually occurred, and the 

 bacteria could be readily seen inside the leucocytes, whereas in 

 fatal ones little phagocytosis took place, if any. He therefore 

 enunciated the paramount importance of the process in immunity, 

 and at one time considered it would cover the whole field of the 

 phenomena. 



But his conclusions did not pass unchallenged, and the sup- 

 porters of the humoral school adduced numerous examples of 

 recovery from infection where little phagocytosis could be 

 observed, and went farther, and showed that recovery might 

 occur under conditions in which phagocytosis was impossible. 

 The best experiments of this sort were those of Baumgarten, 

 which were repeated by Sanarelli. These observers placed non- 

 virulent bacteria in the peritoneal cavities of animals enclosed in 

 bags of collodion or other substances which would permit the 

 free diffusion of the peritoneal fluids, but would prevent the access 

 of the leucocytes, and they found under such conditions that the 

 bacteria were completely destroyed. This was, of course, an 

 example of bacteriolysis of a type with which we are now 

 familiar. Other observers, including Metchnikoff himself, failed 

 to get these results ; but in an experiment of this sort a positive 

 result is of more value than a negative one. It is possible, for 

 example, that the walls of the bags which Metchnikoff prepared 

 may have been sufficiently impermeable to prevent the access of 

 the bacteriolytic substances. Then other observers found that 

 bacteria often underwent changes indicative of death and 

 destruction before they were taken up by the phagocytes. Thus 

 Nuttall found that when attenuated anthrax bacilli were placed 

 in a fine tube in the tissues of a rabbit's ear, the organisms showed 

 degeneration forms before they were taken up by the leucocytes, 

 and thought that they were injured by the serum before being 

 ingested. We have already alluded to this experiment as one of 

 the starting-points of the researches on the alexins. As a result 

 of experiments such as this, the humoralists relegated phagocytosis 

 to a part of quite secondary importance. They held that the 

 injury or death of the bacteria by the humours of the body was 

 the important factor, and admitted only that the phagocytes acted 

 as scavengers to remove the dead or disabled organisms. To 

 this Metchnikoff responded by allowing a leucocyte to take up a 

 living and virulent anthrax spore, and then isolating the leucocyte 



