STUDIES ON THE SERUM OF VACCINATED ANIMALS. 61 



a mixture of the two sera. The sign 4- indicates that a positive 

 granular transformation took place. 



Vibrios. 



Id 



C3 O 



o> a 



Vibrios. 



Eastern Prussia . 



Holland, A, B, C, D, E, F 



Angers 



Dantzig 



Hankin (Agra) 



Polfer : 



Pilon (Saint-Denis, from Netter) 



Inovrazlaff 



Constantinople, A, B, C, D, E, F, 



G, H, I, J, K (Nicolle) 



Cassino. . . 



Hamburg 



Hamburg (Pfeiffer) 



Paris, 1894 -. 



Saint-Cloud 



Vibrio Metchnikovi 



Nordhafen 



Finkler 



Olin (Saint-Denis, Netter) . 

 Sakharoff ) vibr. from Tif 

 Rechtsamer ( Us water. 

 Calcutta. . 



Certain of these vibrios that give Pfeiffer's phenomenon will also 

 show it to a certain extent in normal serum without the addition of 

 cholera serum. These are the slightly virulent vibrios which are very 

 susceptible to the normal protective agents of the animal body. 

 The most remarkable of these organisms in this respect is vibrio 

 " G." from Constantinople. It should be noted, however, that this 

 granular transformation of vibrios by normal serum is always rather 

 limited and is rarely comparable to that caused by the normal serum 

 plus cholera serum. As a general rule the addition of a very small 

 amount of preventive serum suffices to produce the phenomenon 

 in vitro. The technique that we usually employ is the following: 

 A drop of 24-hour culture suspended in 6 c.c. of salt solution is 

 placed on a slide; to this drop is added a loop of anticholera serum. 

 To one drop of this mixture is added a similar drop of normal serum. 

 A slightly larger amount of serum is necessary to cause the phenom- 

 enon in Pfeiffer's organism or in the vibrio from Saint-Cloud. 

 It is not surprising, however, that certain varieties should resist 

 better than others. 



Vibrios that do not give the phenomenon in vitro also fail to give 

 it when injected with cholera serum into the peritoneal cavity of 

 animals. There is therefore complete correspondence between these 

 in vitro experiments and experiments in the living animal. This 

 method, then, may certainly be utilized as simpler and less expen- 



