STUDIES ON THE SERUM OF VACCINATED ANIMALS. 71 



from an immunized animal, necessary to add to the preventive 

 substance is in either case little and, within broad limits, apparently 

 the same. It seems evident, then, that the bactericidal substance 

 in immune serum is not sensibly greater in amount than in normal 

 serum. 



VI. Leucocytic Secretions and Pfeiffer's Phenomenon. 



Experiments that have been given in a previous article* showed 

 us that during life the bactericidal substance is within the leucocytes. 

 When blood is taken out of the vessels this substance is liberated in 

 the surrounding medium and endows the serum with bactericidal 

 properties. Both serum deprived of some of its leucocytes, and 

 edema fluid, are less bactericidal than serum obtained under normal 

 conditions. They are also less preventive. It is easy to determine 

 whether edema will produce Pfeiffer's phenomenon when added to 

 preventive serum. Hanging drops are prepared containing on the 

 one hand, cholera vibrio, preventive serum and serum of a nor- 

 mal guinea-pig; and, on the other hand, cholera preventive serum 

 and edema fluid from the same normal guinea-pig. These mixtures 

 are prepared in the usual manner, so that the doses are equal in each 

 preparation. 



It is to be noted that edema fluid causes no Pfeiffer's phenomenon. 

 It is evident that the bactericidal substance in this fluid is too 

 small in amount, since there is complete transformation in the prep- 

 aration containing serum. In the same manner it may be deter- 

 mined that goat milk, aqueous humor from the guinea-pig, and 

 urine, tears, or saliva (human) when added to preventive serum 

 produce no metamorphosis of vibrios. Edema fluid from a guinea- 

 pig infected with anthrax, and pleural exudate from a guinea-pig 



* See page 24 et seq. 



