130 STUDIES IN IMMUNITY. 



Another poinl which constantly recurs is the more or less distinctly 

 superior phagocytic activity of the mononuclears over the mi- 

 crophages particularly to be noted in beginning phagocytosis. 

 Another regular finding is a relation between the consistency of the 

 exudate and the occurrence of phagocytosis. 



In exudates containing large numbers of leucocytes and bac- 

 teria there an- often to be found, before partial phagocytosis begins, 

 localities where cells are collected in more or less compact masses; 

 these leucocytes frequently show changes; their protoplasm is not 

 distinctly outlined and they are frequently confluent; these clumps 

 are surrounded by a slimy layer that does not stain well; this layer 

 is apparently mucilaginous and has some distinct relation to 

 cellular disintegration. Within this layer there are large numbers 

 of streptococci to be found that are small and 'poorly colored, in 

 other words that show distinct evidence of abnormality, having 

 apparently developed there and been retained by the more fluid 

 nature of the exudate at this point. 



When taken from the body the exudate coagulates, the leucocytes 

 are killed and the fluid therefore becomes distinctly bactericidal. 

 B. Delayed complete phagocytosis. — In order for a complete 

 phagocytosis to take place it is necessary for the bacteria to be in 

 not too great numbers and for the animal not to be too exhausted. 

 The pre-phagocytic period is similar to the corresponding period 

 in incomplete phagocytosis, but is not so long. When the animal 

 survives, a progressive diminution in the number of living bac- 

 teria within the phagocytes is to be noted day by day; the cocci 

 inside the phagocytes are separated. 



The phagocytic activity in complete phagocytosis is very great, 

 not only on the part of the mononuclears, but also by the polynu- 

 clears. The macrophages do not content themselves with taking 

 up streptococci, but also take up more or less degenerated polynu- 

 clears, which may already themselves have taken up bacteria. This 

 point has already been brought out by Metchnikoff in studying the 

 phagocytosis of the streptococcus in erysipelas. 



There are all transitions between delayed phagocytosis and 

 immediate phagocytosis. The latter, as we have seen, occurs in 

 rabbits immunized by serum and prepared by bouillon on the intra- 

 peritoneal injection of a small amount of streptococcus. Without 



