20 STUDIES IN IMMUNITY. 



that the least phagocytosis takes place and that here especially 

 the vibrio will be killed and disappear entirely, apart from any 

 intervention of the cellular protoplasm. 



It may indeed be shown that the serum of a rabbit vaccinated 

 against cholera is more bactericidal than its peritoneal exudate. 



Before considering the experiments that we have performed on 

 this subject, it might be well to recall briefly the method of deter- 

 mining the relative bactericidal power of body fluids and the means 

 of ascertaining which of two fluids or of two sera, to be exact 

 is the more destructive for a given micro-organism. 



Small carefully measured amounts of the fluids to be compared 

 (1 c.c. for example) are placed in separate test tubes. The growth 

 of the organism, which, let us say, is a culture of cholera on agar, is 

 suspended in a few cubic centimeters of salt solution (0.6 per cent) 

 or of bouillon. The first of the sera is inoculated with a platinum 

 loop of this culture dilution. The loop is agitated in the fluid with 

 extreme precaution to distribute uniformly all the bacteria intro- 

 duced; this serum has then become a homogeneous medium con- 

 taining the organisms. A small amount of this inoculated serum 

 is then carefully withdrawn by means of the loop and carried over 

 into a tube containing fluid gelatin at body temperature. The 

 gelatin is then shaken to scatter the inoculated organisms, and 

 poured into a Petri dish. (First culture.) 



The number of colonies that develop indicates relatively exactly 

 the number of bacteria contained in a loop of the inoculated serum. 

 Since the operation has been carried out rapidly, the micro-organisms 

 carried over to the gelatin have been in contact with the serum for 

 a short time only, and whatever bactericidal power the serum may 

 possess has not had sufficient time to affect them. After a certain 

 time the same amount of serum, measured accurately by means of 

 the same loop, is again withdrawn. A second gelatin plate is inocu- 

 lated. (Second culture.) If the serum is bactericidal, this second 

 plate should contain either less colonies than the first, or perhaps 

 none at all. If we repeat successively at intervals the same 

 procedure, we shall have gelatin plates that will give us an indi- 

 cation of the number of micro-organisms remaining alive in the 

 serum. 



If the same set of manoeuvres is performed in an identical manner 



