STUDIES ON THE SERUM OF VACCINATED ANIMALS. 77 



tericidal substances, which, although strong within the leucocytes, 

 are necessarily weakened when liberated into the serum. When 

 phagocytosis of the cholera vibrio by the leucocytes of a well- 

 immunized animal is studied in vitro the granular transformation 

 of the organism and its changes in color reaction are found, not only 

 in the leucocytes, but also in the surrounding fluid. When such an 

 experiment is made with the diphtheria bacillus and the leucocytes 

 of a guinea-pig immunized the day before by a large dose of anti- 

 diphtheria serum (3 c.c), it is found that the organisms within the 

 leucocytes lose their power to stain blue and take eosin, whereas 

 outside the leucocytes the bacteria show no tinctorial change. In 

 other words, the activity has remained within the protoplasm of the 

 phagocyte. It is well known, moreover, as Behring has shown us, 

 that the body fluids of animals immunized against diphtheria have 

 no effect on Loffler's bacillus, which differs from the findings in the 

 case of cholera. And, although there is apparently a different set 

 of facts to consider in each of these cases, it is to be noted that ener- 

 getic bactericidal activity on the part of the phagocytes occurs in 

 both instances. 



If there is a distinction, then, to be drawn between bactericidal 

 sera and those that are not, it is due to a difference in resistance of 

 the specific organisms and not to the absence or presence of a 

 bactericidal substance in the serum. 



The best evidence of this fact is that the more strongly animals 

 are immunized the more frequently do we find examples of the 

 humoral bactericidal activity and extracellular destruction of 

 bacteria. In other words, the destructive function has been 

 increased to such a point that it is manifest even outside the 

 phagocytes. The use of highly immunized animals was necessary 

 to discover Pfeiffer's phenomenon. Later Pfeiffer * and Dunbar f 

 found that the typhoid bacillus also shows granular transformation 

 when injected into the peritoneal cavity of an animal together with 

 a certain amount of preventive serum. Dunbar has noted similar 

 facts with phosphorescent vibrios and Bacillus pyocyaneus. These 

 observations agree entirely with those originally made on the 



* Pfeiffer, Deutsche medicinische Wochenschrift, No. 48, 1894. 

 f Dunbar, Zum Stande des bakteriologischen Cholera Diagnose. Deutsche 

 medicinische Wochenschrift, February, 1895. 



