STUDIES ON THE SERUM OF VACCINATED ANIMALS. 49 



itself immediately after inoculation it will soon find itself opposed 

 by a large number of invaders and resistance will be useless. The 

 rapidity of defense then is of considerable importance in the cure; 

 the slightest influences that hasten the reaction against an infection 

 may decide the issue of the combat. Injections of bouillon and of 

 normal serum are preventive only by increasing slightly the bacte- 

 ricidal property and by attracting leucocytes. These slight pre- 

 ventive properties suffice to cause the animal defense to begin 

 immediately and so protect the animal. A cure which in itself is 

 of vital importance may be effected by agents in themselves insig- 

 nificant. There is no comparison to be drawn between the preven- 

 tive power of these inert fluids and that of a specific serum, and it is 

 unsafe to judge of the preventive power of a fluid simply by the 

 results which it produces. For example, the immune serum against 

 the vibrio Metchnikovi has an energetic attraction for guinea-pig 

 leucocytes. If this serum is injected into the peritoneal cavity it 

 may consequently attract leucocytes and thus prepare the animal 

 for a defense against any vibrio that may subsequently be injected. 

 The most important result caused by such an injection, however, is 

 the genesis of an energetic bactericidal power against the vibrio 

 Metchnikovi which endows the leucocytes with a strong destructive 

 power for this vibrio. But this latter bactericidal power, which is 

 so effectual against the vibrio Metchnikovi, is useless against the 

 cholera vibrio. 



EXPERIMENT 15. A small amount of blood was taken from a 

 normal guinea-pig (serum I). The animal was then given intraperi- 

 toneally 1 c.c. of serum from a guinea-pig vaccinated against the 

 vibrio Metchnikovi; 24 hours later a small amount of blood was 

 again withdrawn (serum II). The bactericidal properties of these 

 two sera against the vibrio Metchnikovi and against the cholera 

 vibrio (Eastern Prussia) were then determined by the plate method. 



