182 BACTERICIDAL OB, ANTI-BACTERIAL IMMUNITY. 



Several years ago, Pfeiffer showed that the blood serum of a guinea- 

 pig, artificially immunized against the cholera vibrio, was capable, under 

 certain conditions, of not only immobilizing and killing cholera germs in 

 a short time, but also of causing their disintegration and destruction, 

 This significant capacity of immune serum was, after a long series of ex- 

 periments, finally found to be due to two distinct substances. One of 

 these appeared to be formed in the body, as the result of the gradual 

 adaptation of the animal to the cholera microbe, and was called the im- 

 mune substance. The other seemed to be normally present in the serum 

 of the warm-blooded animals, and to be identical with the substance 

 which had long been regarded as in itself germicidal, and which had 

 been called by Buechner alexin. It was presently found that lysis of the 

 cholera microbe occurred only when these two substances act together, 

 neither of them when separate having lytic power. If the two substances, 

 the immune substance and the alexiu, lytic when together, are heated to 

 56 C., the lytic capacity is lost. But if a small amount of fresh blood 

 serum containing alexin be now added, the lytic power is at once re 

 stored. These curious facts, set forth in part by Pfeiffer and further 

 developed by Bordet and Metschuikoff, obviously have an important 

 bearing upon our conception of the processes by which those phases of 

 immunity are secured in which the destruction of micro-organisms plays 

 an important part. 



But the study of the effects of lytic sera upon bacteria is one of great 

 technical difficulty, so that it is only since an important series of obser 

 rations were made upon the lytic action of the body fluids on other and 

 more easily studied forms of cells, that our conception of the nature of 

 bacteriolysis has become at all clear. 



It is therefore necessary for us to look briefly at a new line of research 

 bearing upon bacteriolytic immunity which has already led to most 

 significant results and opened biological fields of great scope and com- 

 plexity. 



Cytolysis. It has been known for some time that the blood serum of 

 one animal species, when injected into the vessels of another, may do 

 serious damage and even kill the latter through a rapid separation of 

 the haemoglobin from the red blood -corpuscles. This dangerous effect 

 brought to a speedy end attempts which were at one time made to sustain 

 the ebbing forces of life by the transfusion of alien blood, But the sig 

 nificauce of this so-called "laking" of the blood by mixture with alien 

 sera was overlooked. 



Bordet, however, was recently led to inquire whether if the animal 

 body be capable of adapting itself to toxic substances and to bacteria in 

 such a way as to neutralize the effects of toxins and to destroy bacteria, 

 as had been shown by earlier experiments, it may not respond similarly 

 to the introduction of other foreign substances, such as alien red blood 

 cells, for example. 



The blood serum of the guinea-pig is not normally lytic for the red 

 blood cells of the rabbit ; that is, it does not cause the separation of the 



