STUDIES ON THE SERUM OF VACCINATED ANIMALS. 



55 



EXPERIMENT 17. A small amount of blood was taken from a 

 normal guinea-pig (serum I). One twentieth of a cubic centimeter 

 of an old culture of cholera vibrio (Eastern Prussia) was then in- 

 jected into the peritoneal cavity. Twenty-four hours later another 

 specimen of blood was taken (serum II) . The bactericidal property 

 of the two sera against the vibrio was then determined by gelatin 

 plates. 



NUMBER OF COLONIES. 



As is seen from this experiment the bactericidal power is not 

 increased. It is probable that the injection of small amounts of 

 culture produces a relative immunity due to the attraction such 

 substances have for leucocytes. If preventive substances owe their 

 origin to bacterial products, as their specificity would indicate, it 

 is not owing to any direct relation between the two, but on account 

 of some elaboration on the part of the animal body. 



