170 INFECTION AND RESISTANCE 



conclusive, since at the time when these investigations were carried 

 out no discrimination was made between the bactericidal serum sub- 

 stances and those other "endolysins" which might well have been 

 extracted from the accumulated white blood cells. The writer some 

 years ago attempted to approach this problem directly by keeping 

 leukocytes alive in inactivated serum and in Ringer's solution at 

 37.5 C. for several days in the hope that, after 48 hours, alexin, 

 hemolytic or bactericidal, might appear in these fluids. The experi- 

 ments were entirely negative, but were regarded as inconclusive, since 

 it was impossible to determine accurately how long, or in what pro- 

 portion, the leukocytes had remained alive. 



One of the basic premises of MetchnikofFs theory on the nature 

 of alexin consists in the conception that alexin is not found in the 

 circulating blood plasma, but appears only when there has been leu- 

 kocytic injury, as in the clotting of blood or in the "phagolysis" 

 which, as we have seen in the chapter on phagocytosis, usually occurs 

 after foreign substances have been injected into the peritoneum, pre- 

 ceding a local accumulation of leukocytes. This point of view seems 

 to be rendered improbable because of the rapid hemolysis which 

 occurs when we inject sensitized red blood cells into the circulation 

 of an animal, but we might here, too, assume a preliminary injury 

 to white blood cells resulting from the intravenous injection. 



Much less likely to be accompanied by cell injury is the method 

 of obtaining blood serum by creating an area of artificial edema by 

 ligating a limb or, as in MetchnikofFs 9 10 experiments, the ear of 

 a rabbit. And, indeed, in edema fluids so obtained little or no alexin 

 is ordinarily found. This fact has been interpreted in favor of 

 MetchnikoiPs views, as has also the curious absence of alexin in the 

 aqueous humor of the anterior chamber of the eye. 11 12 In this fluid 

 no alexin is present under normal conditions, but if puncture is prac- 

 ticed, and the fluid again taken after a period of three or four hours, 

 alexin is now found, probably, according to Metchnikoff s school, be^ 

 cause of the coincident entrance of leukocytes into this space. It is 

 conceivable, however, that the aqueous humor may be free from 

 alexin for other reasons than the absence of leukocytes ; and an injury 

 which is followed by the invasion of leukocytes is pretty sure to be 

 followed also by the entrance of the fluid elements of the blood ; i. e., 

 alexin. 



Much experimental work has been done in which it has been 

 attempted to demonstrate directly that the blood plasma contains no 

 complement or alexin. The most important investigation of this 



9 Metchnikoff. Ann. Past., Vol. 9, 1895. 



10 Bordet. Ann. Past., Vol. 9, 1895. 



11 Metchnikoff. Loc. cit. 



12 Mesnil. Ann. Past., Vol. 10. 



