STUDIES ON THE SERUM OF VACCINATED ANIMALS. 37 



B. pyocyaneus. — Distinct phagocytosis. Some of the organisms 

 within the phagocytes are colored a faint pink. 



B. ramosa and the red bacillus of Kiel. — Similar phenomena. 



Streptococcus. — Polynuclear leucocytes capture large numbers 

 of streptococci. Within 4 hours the majority of the cocci taken up 

 still stain blue. There are to be noted, however, in some phagocytes, 

 chains of red streptococci; at times one or two of the cocci in a 

 chain remain blue or violet. 



It is evident that the same phenomena may be observed in vivo 

 as in vitro. For example, we have injected the diphtheria bacillus 

 (1 c.c. of a 24-hour bouillon culture) into two guinea-pigs, one 

 of which had received the day before 3 c.c. of bouillon in the 

 peritoneal cavity, and the other of which had received 3 c.c. of 

 anti-diphtheria serum. The injection of bouillon produced a rich 

 leucocytic exudate composed largely of polynuclears, but also con- 

 taining a few mononuclears. In the animal injected with preventive 

 serum, the exudate contained many polynuclears, but, in addition, 

 a number of mononuclears (macrophages). In both animals 

 phagocytosis is noted after injection of the culture, and, as is usual, 

 the polynuclears seem to take the greater part in it. In the case 

 of the guinea-pig vaccinated with serum, however, the macrophages 

 are found to have taken up considerable numbers of organisms. 

 After an hour there are numerous intraphagocytic bacilli staining 

 red both in the animal that had received bouillon and in the one 

 immunized with serum. Although the taking up and destruction 

 of the organisms appears to go on without any difficulty, there 

 remain certain resistant bacteria, so that positive cultures were 

 obtained from the exudates of both animals 18 hours after injection. 



The uniformity with which phagocytosis occurs even when 

 leucocytes have been taken out of the animal body and are no 

 longer in their normal condition is amply proved by these experi- 

 ments.* Changes of the bacteria in cells are always noted. One 



* The activity of phagocytes against bacteria in vitro gives a means of studying 

 the effect of different poisons, toxins or drugs on these cells. Active substances 

 may be added to leucocytes and then, after varying periods of time, bacteria may 

 also be added. We are at present engaged in studies along this line. We are 

 rather surprised to find that diphtheria toxin, which kills the guinea-pig in a dose 

 of 0.2 to 0.1 of a cubic centimeter, produces no effect on the phagocytic activity 

 of the leucocytes of this animal. 



