482 IMMUNITY. 



quantity of normal serum played the same part as fresh peritoneal fluid. 

 His method was the following : 



(a] An emulsion of the living organisms (for example of the cholera 

 vibrio) was made by adding a young culture to about 5 c.c. of bouillon ; 

 (b) two drops of this emulsion were taken, and mixed with a small 

 drop of anti-cholera serum ; (c) a drop of this mixture was taken, and 

 there was added to it a drop of equal size of fresh serum from a 

 normal guinea-pig. A hanging-drop preparation was made, and a 

 change similar to that described by Pfeiffer was observed within one to 

 two hours if the preparation was kept at the temperature of the body. 



Bordet found that in every case in which Pfeiffer's reaction 

 took place within the body of an animal, a similar lysogenic 

 reaction could be observed by his method outside the 

 body. He considers that the reaction depends upon the 

 presence of a specific immunising substance in the anti- 

 serum which greatly increases the bactericidal power of the 

 normal serum, but that in most cases this specific substance 

 cannot lead to the destruction of the organisms without the 

 aid of healthy serum. Bordet and MetchnikofT hold the 

 source of the specific protective substance as well as that of 

 bactericidal substances to be in the leucocytes. 



Agglutination. Charrin and Roger had previously (1889) 

 observed that when the bacillus pyocyaneus was grown in 

 the serum of an animal immunised against this organism, 

 the growth formed a deposit at the foot of the vessel ; 

 whereas a growth in normal serum produced a uniform 

 turbidity. Gruber and Durham, in investigating Pfeiffer's 

 reaction, discovered an analogous phenomenon. They 

 found that when a small quantity of the serum of an animal 

 highly immunised against a particular motile organism 

 (cholera vibrio, typhoid bacillus, etc.) is added to an 

 emulsion of the organisms, the latter lose their motility, 

 and become agglutinated into clumps. In a small test-tube 

 a reaction in this way occurs which is visible to the naked 

 eye, a sort of precipitate forming which consists of masses 

 of non- motile organisms. The higher the degree of 

 immunity, the smaller is the amount of serum necessary to 

 bring about this phenomenon. The specific substance in 

 the serum, therefore, has a direct action on the organisms, 



