IMMUNITY. 217 



the makrophages; with this influence, however, the power of the 

 opsonins seems to terminate, for the makrophages of the im- 

 mune animal do not seem to destroy the bacilli more quickly 

 than the normal one. It may be that the opsonins indirectly 

 protect t.he immune animal, since where phagocytosis is active 

 the endotoxins are liberated inside the phagocytes, and not in 

 the circulating plasma. 



Neufeld and Rimpau* found that antistreptococcus serum 

 acts as an opsonin. 



Just the contrary effect to opsonins, on the other hand, is 

 produced by certain other bodies; for Bailf has found that 

 when tubercle bacilli undergo bacteriolysis certain substances 

 are liberated which check phagocytosis. These he regards as 

 endotoxins, and gives to them the name aggressins. 



There can be no doubt but that phagocytosis plays an im- 

 portant part in combating bacterial infection. And what fol- 

 lows in regard to the germicidal and antitoxic action of the 

 fluid portion of the blood containing no phagocytes does not 

 alter the fact that phagocytes, when these are present, do de- 

 stroy the bacteria. Moreover, Metchnikoff maintains that 

 the germicidal property of the blood-serum free from cells is 

 due to substances liberated from the phagocytes by phagolysis, 

 or breaking up of phagocytes. In other words, he holds that 

 infection is combated by the phagocytes or by substances de- 

 rived from the phagocytes. 



But be this as it may, it is well established that the serum of 

 the blood deprived of leukocytes also has the property of de- 

 stroying bacteria in many cases. The effect produced upon 

 the bacteriolytic property of the blood-serum by injecting the 

 animal from which the serum is obtained with bacterial cul- 

 tures has already been stated (page 210). 



*Deutsche medicinische Wochenschrift. 1904. Bd. XXX., p. 1458- 

 tOskar Bail. Wiener klinische Wochenschrift. Bd. XVIII., 1905. Re- 

 view in Bulletin de I'Institut Pasteur. III., p. 348- I9°5- 



