IMMUNITY. 189 



Disintegration of leucocytes may give rise to the presence 

 of complement in the serum. 



An example of the destruction of bacteria in immunized 

 animals is seen in an experiment performed by Pfeiffer. A 

 guinea-pig is given repeated injections of the spirilla of 

 cholera, which have been killed by chloroform or heat. 

 When living spirilla are introduced into the peritoneal 

 cavity of such an immunized guinea-pig they rapidly 

 undergo disintegration. Since no such disintegration takes 

 place when other bacteria than the spirilla of cholera are in- 

 jected into the animal made immune from this organism, it 

 has been suggested by Pfeiffer that this reaction could be 

 made use of in the diagnosis of that disease. If the serum 

 of the immune animal be introduced along with the cholera 

 spirilla into the peritoneal cavity of an animal not immune, 

 the same disintegration takes place. Furthermore the serum 

 of the immune animal may be heated to 70 C. and will still 

 cause disintegration of the organisms in the peritoneum 

 of a non-immune guinea-pig. The heated serum alone is 

 found inactive. The explanation of this phenomenon ap- 

 pears to be that the serum of the normal animal contains 

 the complement only. The serum of the immunized animal 

 has developed in it the intermediary or immune body, besides 

 the normal complement. The immune body resists heat, 

 while the complement is destroyed by heat. The previously 

 heated serum from the immunized animal, mixed with 

 organisms, finds the necessary complement in the normal 

 animal. The organisms then become disintegrated. 



Such disintegration of bacteria is called bacteriolysis. 

 The substances which effect it are called lysins. It is prob- 

 able that the development of lysins is one of the most im- 

 portant factors in checking infections and in promoting 

 recovery. The preparation of specific bacteriolytic blood- 

 serum from immunized animals has been attempted for the 



