PFEIFFER'S EXPERIMENT 71 



complement alone possesses no hemolytic properties. That ambo- 

 ceptor by itself is similarly inactive is proved by the fact that the 

 treated corpuscles per se will not be hemolyzed when these are 

 suspended in saline. 



Demonstration of Bactericidal Substances in Serum. The mere 

 demonstration of the presence of bactericidal substances in a given 

 serum is a relatively simple matter, while the study of the actual 

 extent of its destructive action meets with difficulties, which are 

 largely owing to the fact that blood serum, while it may be bacteri- 

 cidal, is at the same time a very favorable culture medium, and that 

 within certain limits bacterial destruction and bacterial reproduction 

 go hand in hand. The values which are thus obtained are hence of 

 necessity relative values only, and in reality merely express to what 

 extent cell destruction predominates over cell formation. 



Whether or not a given serum contains bactericidal substances 

 can be determined either by direct microscopic examination, i. e., by 

 inoculating tiny little tubes of fresh serum with very small amounts 

 of a certain organism (cholera vibrio, best) and observing the result- 

 ant suspensions in the hanging drop after a brief incubation at 37 C., 

 or by intraperitoneally inoculating a guinea-pig weighing about 200 

 grams with a very small quantity of an agar culture (less than yV 

 milligram = -^V oese in suitable dilution in the case of a virulent 

 culture of the cholera vibrio), when specimens of the peritoneal fluid 

 are removed by means of glass capillaries at intervals of 10, 20, or 

 30 minutes, etc., and examined either directly in the hanging drop 

 or after staining, in the dried smear. With either method it will be 

 observed that the organisms at first lose their motility and then 

 contract to little granules which in the beginning are highly refrac- 

 tive, but gradually become paler and paler, until they dissolve alto- 

 gether. At first the granules can still be stained with anilin dyes, 

 but as the process of destruction proceeds they become paler and 

 paler, until at last they are no longer demonstrable. As Wassermann 

 very appropriately remarks, the granules melt away like wax in 

 boiling water. 



Pfeiffer's Experiment. Still more striking results will be obtained 

 if the animal is simultaneously injected with a small quantity (about 

 1 milligram) of serum from another animal which has been previously 

 rendered highly immune against the organism in question by vaccina- 

 tion (which see). In such a case a much larger quantity of bacteria 



