154 PHYSIOLOGY CHAP. 



The haemolytic or globulicidal toxic action of heterogeneous 

 blood depends rather upon the plasma than on the blood-corpuscles. 

 Approximately the same effect is produced by injection of 

 heterogeneous serum (Landois). 



(c) The capacity of the blood, or serum, to destroy the foreign 

 cellular elements that penetrate it, is intimately connected with 

 another, and, from the medical point of view, far more important 

 of its properties viz. destruction of certain pathogenic bacteria ; 

 this constitutes a natural defence of the body against special 

 infectious diseases, and is even more important than the phagocytosis 

 attributed to the leucocytes. 



Fodor (1887) and then Nuttall and Flugge (1888) were the first 

 to demonstrate the bactericidal properties of the blood of living 

 healthy animals. H. Buchner (1889) showed that these depend on 

 the very unstable proteins of the plasma, which derive from the 

 metabolic activity of the leucocytes or other cells, and which he 

 designated by the name of alexins (from aAef^o-is, defence). He 

 found that the serum lost its bactericidal property on simple 

 dialysis with water, but not with physiological salt solution. 



By this treatment the serum only loses its salts ; yet after the 

 restoration of its original molecular concentration it does not 

 recover its bactericidal activity. This is perhaps due to the fact 

 that the salts before dialysis are in some way bound up with the 

 proteins, which association, on account of its great instability, 

 cannot be reinstated when once disturbed by dialysis. The serum 

 also loses its bactericidal effect on warming to 55 C. for an hour 

 or to 52 C. for six hours, a fresh proof of the great lability of the 

 alexins. 



The bactericidal action of one kind of blood is not common to 

 all other species, nor does it extend to all bacteria, only to certain 

 of them. Thus, e.g., the serum of human blood contains alexins 

 against the bacteria of typhoid and cholera, while it has less effect 

 upon StapTiylococcus pyogenes, and none on streptococci and the 

 diphtheria bacilli and anthrax ; the serum of the rabbit and dog 

 will kill typhoid bacilli, while the serum of the calf and horse 

 have not this power (Buchner) ; the serum of the rat kills anthrax 

 bacilli, while the serum of mouse, guinea-pig, rabbit and sheep has 

 no bactericidal effect upon them (Behring). 



Yet more wonderful is the fact, which has been recognised for 

 some time, that recovery from certain infectious diseases is followed 

 by immunity to them. Behring and Kitasato (1890) discovered 

 the cause of this phenomenon to be that the said infections 

 develop as an after-effect (in the blood of those persons who 

 survive them) a previously non-existent property of rendering 

 the bacterial toxins innocuous. They further showed that if 

 the serum of an individual who has become immune to any given 

 infection be injected into other individuals in sufficient doses, 



