STUDIES ON THE SERUM OF VACCINATED ANIMALS. 27 



Our experiments have been carried out largely with two cholera 

 vibrios: the vibrio of Massaouah, isolated by Pasquale, and the 

 vibrio from Eastern Prussia. We shall not consider here whether 

 or not the vibrio of Massaouah is of the same variety as the typical 

 Koch vibrio. The researches of Pfeiffer would indicate that there 

 are characteristic differences between cholera vibrios from different 

 sources, which would lead us to think that they do not all belong to 

 the same strain of bacteria. It would appear that there are several 

 varieties of cholera vibrios and that one of these varieties which is 

 widely distributed and is of great importance is represented by 

 Koch's vibrio. This organism, according to Pasquale, is the sole 

 cause of epidemics. However that may be, animals immunized 

 against the vibrio of Massaouah have energetic specific pre- 

 ventive and bactericidal properties in their sera and therefore 

 fulfill the conditions we desire. What is more, this vibrio has the 

 advantage of being highly virulent and relatively constant in its 

 pathogenicity. 



We have tried to effect a separation between the blood fluid and 

 the blood cells in an animal vaccinated against cholera. For this 

 purpose it was necessary to obtain a more or less cell-free plasma, 

 and we succeeded in doing this by causing an edema of the leg or 

 ear by venous compression. The edema fluid represents blood 

 plasma filtered under pressure and almost completely deprived of 

 cells. The walls of blood vessels are not sufficiently impermeable 

 to hold back all the cells, and the fluid obtained in this manner con- 

 tains a few red blood cells and very infrequent leucocytes. A com- 

 parison may be made between fluid obtained in this manner and 

 the serum of the same animal as regards their respective bactericidal 

 powers. The serum is obtained by spontaneous coagulation of the 

 whole blood containing many cells. If during life bactericidal 

 substances remain within the cells and appear in the blood fluid 

 only after removal from the body and coagulation, a distinct dif- 

 ference should appear between these two fluids. 



Experiment 5. A rabbit weighing 1790 grams was vaccinated 

 against the Vibrio Massaouah. The serum of this rabbit was tested 

 for bactericidal and preventive properties and found to be markedly 

 bactericidal. One-fifth of a cubic centimeter moreover protected 



