14 STUDIES IN IMMUNITY. 



then increases rapidly. After 3 hours, for example, it is found that 

 the exudate is very rich in polynuclears. These cells are far more 

 than are required to take up alkthe organisms present; as a matter 

 of fact, only a relatively small number of cocci were injected and 

 these have had no opportunity to increase. But no matter how 

 numerous the phagocytes are, free organisms which have escaped the 

 destructive phagocytic action are still found in the surrounding fluid. 

 Only a certain number of them have become the prey of the white 

 corpuscles. 



Then a second phase of the infection begins. The number of micro- 

 phages continues to increase. At the same time the organisms that 

 have not been taken up multiply and give rise to new individuals. 

 At the end of 6 hours the exudate is seen to contain very large 

 numbers of phagocytes and at the same time a considerable num- 

 ber of organisms. But these phagocytes are empty. The phago- 

 cytosis of the coccus noted at first is no longer present. This fact 

 is still more surprising since the organisms and the phagocytes must 

 still be in contact; it would seem as if the tactile reaction which 

 the cells usually show would suffice to produce phagocytosis. 



It must be that some active influence prevents the phagocytes 

 from taking up those organisms scattered about them. What is 

 this influence? Two explanations occur: (a) either the leucocytes 

 are paralyzed by the toxin that the streptococcus secretes in multi- 

 plying; or, (6) the leucocytes, while retaining all their motility and 

 facility for taking up organisms, may have been subjected to a nega- 

 tive chemiotactic influence from the streptococcus that prevents 

 them from taking up the bacteria. We shall see that the first of 

 these hypotheses is incorrect. The second is the true explanation. 



Eight hours after injection, when the animal appears to be very 

 sick and the peritoneal exudate is alive with organisms and very 

 rich in phagocytes, we give a second injection. We inoculate 1 c.c. 

 of a rich bouillon culture of Proteus vulgaris (24 hours old); this 

 organism is only slightly virulent and is easily destroyed by phago- 

 cytes. A few moments later, if we take out a little exudate, we 

 find that the cells which refuse to take up the streptococcus have 

 eagerly taken hold of the new organism offered them. Within a 

 half hour almost the entire culture is within phagocytes. It is 

 extraordinary how these phagocytes have chosen between the two 



