CONTRIBUTIONS TO THE STUDY OF IMMUNITY. 45 



phages yield this to the blood at_ the end of their intracellular diges- 

 tion. Metchnikoff bases this view chiefly on his observations that the 

 destruction of avian blood-cells in the peritoneal cavity of normal 

 guinea-pigs is effected exclusively by the macrophages. 



This statement is in direct opposition to mine, according to which 

 even in untreated animals, the solution takes place free in the peri- 

 toneal exudate independently of the phagocytes. I believe, however, 

 that these apparently contrary results can well be harmonized. 



According to Metchnikoff the solution of goose blood-cells in 

 the subcutaneous connective tissue of even non-immunized animals, 

 is effected almost exclusively extracellularly. Haemolysis in this 

 case must be due to a passage of complement and interbody from 

 the blood into the subcutaneous tissues; this will naturally proceed 

 more rapidly when, as a result of substances exciting inflammation, 

 a stronger exudation ensues. 



It would be very curious if the same conditions for the passage 

 of haemolytic substances from the blood were not present in the peri- 

 toneal cavity. We know, for example, that Pfeiffer's phenomenon 

 is especially marked in the peritoneal cavity. As a matter of fact, 

 shortly after an injection of avian blood-cells into the peritoneal 

 cavity of normal guinea-pigs, one always observes free nuclei, even 

 when the serum has been removed from the cells by centrifugation. 

 Of this I convinced myseif by repeated observations. If one employs 

 blood-cells of low resistance (chicken-blood), and these in small 

 doses, they will be degenerated and for the most part dissolved before 

 they are taken up by the macrophages in any considerable number. 

 When blood-cells of greater resistance are employed, and these in 

 larger doses, the solution effected by the body juices will be com- 

 paratively slight and occupy more time. The taking up of these 

 cells by the macrophages, which Metchnikoff in his splendid experi- 

 ments was able to follow into the organs, will then come more to 

 the front. 



If therefore, as a result of experiments in which I used sensitive 

 blood-cells in small doses, I underrated the significance of phago- 

 cytosis, Metchnikoff, through the conditions in his experiments, fell 

 into the opposite error. The truth lies between these views; in 

 the peritoneal cavity, according to the prevailing conditions, haemol- 

 ysis can be effected free in the peritoneal exudate or in the interior 

 of the macrophage. 



In any case, phagocytosis is not essential for the development of 



