STUDIES ON THE SERUM OF VACCINATED ANIMALS. 29 



Although the cholera vibrio grew well in the edema fluid, this fluid 

 showed, during the first few hours, a very distinctive bactericidal 

 property, although less than that of serum. The normal serum also 

 possessed a certain bactericidal property. It is to be noted that 

 the gelatin plate made three or four hours after inoculation from 

 the edema fluid was sterile. It is evident, however, that not all the 

 organisms in this fluid were killed, since the cultures made on the 

 following day showed numerous colonies. It should be remarked 

 in this connection that gelatin is not a very favorable medium on 

 which to grow the cholera vibrio. Vibrios that are slightly weakened 

 but are still alive may fail to grow on gelatin when they grow very 

 well on agar. We have often noted this fact, and a growth on agar, 

 then, must be considered the necessary criterion of the sterility of a 

 sample of inoculated serum. 



Experiment 6. A rubber ring was placed about the fore leg of 

 a guinea-pig vaccinated by sterilized and living cultures of the 

 cholera vibrio from Eastern Prussia. An edema was formed which 

 was withdrawn and found to be slightly reddish in color and to 

 contain a few leucocytes. A specimen of blood was taken contain- 

 ing 11,000 leucocytes per cubic centimeter. The serum and the 

 edema fluid were inoculated with a 24-hour culture of the vibrio 

 (Oriental Prussia). 



NUMBER OF COLONIES. 



The edema fluid was cloudy the next day, and under the micro- 

 scope an enormous number of vibrios were found in it; the serum 

 was clear and contained no bacteria. The edema fluid, however, 

 had sufficient activity to weaken the vibrios during the first few 

 hours and to prevent growth on gelatin. The serum gave no 

 growth on agar. 



The production of edema is the best means of separating the cells 

 from the blood plasma, but there is another method which may be 



