184 PHAGOCYTOSIS 



Negative Chemotaxis. In nearly all infections we find that leuko- 

 cytes are attracted in large numbers into the involved area, i. e., nearly 

 all bacteria give off substances that are positively chemotactic. In cer- 

 tain infections, however, we may find the tissues poor in leukocytes, as 

 exemplified in infections due to the presence of virulent streptococci. 

 This negative chemotaxis is more difficult of explanation. Kantlack 

 doubts the existence of really negative chemotactic action upon leuko- 

 cytes. Verigo 1 . also considers that as yet no actual negative chemo- 

 tactic substances have been satisfactorily demonstrated; certainly no 

 marked example o negative chemotaxis has been shown since methods 

 involving the study of phagocytosis in vitro have been devised. It is 

 true that virulent bacteria appear to repel the leukocytes, but, as 

 Kantlack has pointed out, these are not necessarily examples of nega- 

 tive chemotaxis, and it is probable that the paucity in numbers of the 

 leukocytes about such an area of inflammation is due to their over- 

 stimulation or paralysis and destruction of the powerful ferments that 

 are given off by the bacteria. Thus Metchnikoff has asserted that 

 leukocytes might, after a time, be attracted toward substances that 

 would kill them. Therefore, while leukocytes will migrate freely 

 toward substances that would kill them, they may be destroyed before 

 they reach the inflammatory area, or, having reached there, are promptly 

 destroyed and pass into solution (Fig. 47). 



While it is doubtful, therefore, whether substances are produced by 

 bacteria that actually repel leukocytes, the point has not been definitely 

 settled. If such substances exist, it would appear that they are closely 

 identified with either the endotoxins or the aggressins, the latter being 

 definite secretory products of bacteria that neutralize opsonins and 

 retard phagocytosis. In many instances it is probable that the same 

 substances that exert a positive chemotaxis are, when concentrated, 

 negatively chemotactic, through overstimulation and paralysis of the 

 leukocytes. With diminution in the numbers or vitality of bacteria 

 and dilution of their chemotactic substances, this inhibiting influence is 

 removed and the leukocytes are attracted to the focus of infection, thus 

 explaining in a way those instances in which positive chemotaxis is 

 observed to follow a primary period of negative chemotaxis. 



RESULTS OF PHAGOCYTOSIS 



After phagocytosis has been accomplished, the fate of the engulfed 

 objects depends upon their nature. In general they undergo a process 

 1 Arch. d. med. Exper., 1901, 13, 585. 



