120 STUDIES IN IMMUNITY. 



The latter result may seem astonishing. One might expect 

 rabbits that have received the whole culture to receive some benefit 

 from the serum in the fluid and to be enabled to resist the invasion 

 of the bacteria. But it must be noted that this culture contains a 

 considerable number of bacteria, and experiment shows us that 

 1 c.c. of pure serum fails to protect animals against a much smaller 

 dose of bacteria than is present in a cubic centimeter of such a 

 culture. It is not surprising, then, that the culture is virulent, for 

 it contains too many bacteria in proportion to the serum. 



This experiment that we have just mentioned* 'simply shows 

 that streptococci grown in preventive serum show no deterioration 

 that decreases their virulence in subsequent generations. Does 

 it show, however, that preventive serum when injected into an 

 animal before infection is quite incapable of any enfeebling effect 

 on the subsequently injected steptococci? By no means, for we 

 may imagine that a serum incapable of modifying bacteria in vitro 

 may, when in the tissues, affect them, owing to the additional or 

 combined effect of certain adjuvant factors furnished by the animal 

 body. Have we not seen, for example, that cholera serum which, 

 when kept for some time or heated, is incapable of causing granular 

 transformation in vitro can bring about this modification when in- 

 jected into an animal? We make these reservations on a priori 

 grounds without considering for the moment whether or not they 

 are justified by experimental facts. 



The fluids hitherto examined, that is, normal rabbit serum, and 

 preventive serum either pure or mixed with bouillon or rabbit 

 serum, have no bactericidal effect on the streptococcus. There 

 is a body fluid, however, which shows an evident destructive effect 

 on this micro-organism. It is the clear fluid separated by centrif- 

 ugalizing an exudate rich in leucocytes. The streptococcus grows 

 with great difficulty in this fluid and, as Denys and Leclef have 

 already noted, a destruction of bacteria ensues even when a large 

 amount of culture is inoculated. f If a drop of a young culture is 



* This experiment is similar to those of Metchnioff (1892), Issaeff, and 

 Sanarelli (1893) with the bacteria of hog-cholera, pneumonia and the vibrio 

 Metchnikovi. 



f Denys et Leclef, Sur I'lmmunite" du lapin vaccine" centre le streptocoque. La 

 Cellule, 1895. 



