STUDIES ON THE SERUM OF VACCINATED ANIMALS. 59 



The amount of preventive serum necessary in the experiment may 

 be very small. If the serum is very powerful the slightest amount 

 brings about the phenomenon very well. 



Defibrinated blood is a mixture of serum and cells. Are the cells 

 necessary to produce Pfeiffer's phenomenon? If we mix in a 

 hanging drop a small amount of preventive serum and of perfectly 

 clear normal serum, free from cells, and then add a suspension of 

 cholera vibrios, it is found that the organisms soon give a complete 

 transformation phenomenon. It is evident, then, that the phe- 

 nomenon may occur without the presence of the cellular portion 

 of the blood. We have already noted* that the addition of a 

 small amount of preventive serum, even when heated to 60 degrees 

 or 70 degrees and so deprived of bactericidal power, endows normal 

 serum with strong bactericidal property for the vibrio. We were 

 able to demonstrate this property by the gelatin plate method; we 

 shall also show that it may be demonstrated by the phenomenon 

 of granular transformation. Later on we shall return to a dis- 

 cussion of the relation of this experiment to immunity. Let us 

 consider for the present its practical application as a means of 

 diagnosis of the cholera vibrio. 



III. DIAGNOSIS OF THE CHOLERA VIBRIO BY PFEIFFER'S 

 PHENOMENON IN VITRO. 



It is well known how difficult it is to determine the exact proper- 

 ties of the cholera vibrio and consequently how difficult it is to dis- 

 tinguish it from other similar vibrios. The diagnosis of the cholera 

 vibrio in the dejecta of patients is not of great importance during 

 a declared epidemic of typical cholera. It is quite another matter 

 in isolated cases of choleriform enteritis. It is very important 

 for hygienic reasons under these conditions to be able to say posi- 

 tively whether or not the dangerous organism is present. 



Pfeiffer and Issaeff f claim a specificity in the bactericidal and 

 preventive power of the serum of animals vaccinated against 

 cholera, and the experiments that we have mentioned previously 

 led us to corroborate these conclusions. 



The German scientists have used a serum from animals immunized 



* See p. 47. 



t Pfeiffer et Issaeff, Deutsche medicinische Wochenschrift, No. 13, 1894. 



