106 STUDIES IN IMMUNITY. 



The number of phagocytes gradually becomes increased; the 

 cells become infinitely more numerous than is necessary to take up 

 all the streptococci present. There always remain, however, cer- 

 tain free bacteria and these bacteria soon multiply. These organ- 

 isms are differentiated by the fact that they are surrounded by an 

 areola never present under normal conditions, which takes a pale 

 pinkish-violet color with Kiihne's blue. These organisms after 2 

 or 3 hours give rise to new individuals also surrounded by an 

 areola, similarly able to avoid engulfing, and usually occurring in 

 the form of diplococci or in short chains. The number of these 

 new bacteria, as a rule, becomes considerable in 6 or 7 hours. 

 In an exudate taken at this time we find both a large number of 

 cells and a large number of bacteria. The majority of the phago- 

 cytes, however, are empty and no longer capable of capturing bac- 

 teria. We have already shown in a previous article* that such 

 leucocytes not only are not paralyzed, but are, on the contrary, even 

 more motile than usual and are still able to engulf other phagocyt- 

 able micro-organisms, such as the B. diphtheria? or the B. proteus 

 vulgaris. If a culture of Proteus or Diphtheria is added to such an 

 exudate, the leucocytes immediately take up the new bacteria, 

 although they still refuse streptococci; in other words, they choose 

 between the species of bacteria. Streptococci, then, secrete a sub- 

 stance which, although it does not inhibit the influx of leucocytes 

 into the peritoneal cavity, affects adjacent phagocytes unfavorably 

 and prevents them from accomplishing their protective engulfing 

 function. We may say that they exercise a negative cJiemiotactic in- 

 fluence on the phagocytes. The number of these cells increases until 

 it becomes enormous and, as a rule, the guinea-pig dies in from 15 

 to 20 hours with a purulent peritonitis accompanied by an invasion 

 of the heart's blood by the bacteria. The leucocytes retain their 

 faculty of engulfing other micro-organisms for a long time. So far 

 as the extracellular streptococci are concerned they stain well, 

 are morphologically normal, are surrounded by an areola and show 

 at no stage the slightest evidence of degeneration. 



A non-fatal dose. If a smaller amount of culture, for example, 

 0.1 of a cubic centimeter, is injected intraperitoneally in a guinea- 

 pig instead of the minimal lethal dose rapid and complete phagocytosis 



* See page 14. 



