Charles Todd 125 



All the immunity reactions which are known appear to depend 

 upon the fundamental fact that when a foreign protein is injected 

 into an animal, the organism responds by the formation of an 

 "antibody" which is specific for the protein injected. This specificity 

 is extraordinarily complete and the relation between the protein and 

 the corresponding antibody has been compared to that existing between 

 a complicated lock and its key. It appears to be a sine qua non that 

 the injected substance should be a colloid, and carbohydrates, fats etc. 

 do not give rise to the formation of antibodies. 



If half a dozen different foreign proteins be injected into an animal 

 at the same time, the corresponding six antibodies duly appear in the 

 serum ; and it is difficult to suppress a feeling of astonishment at the 

 perfection of a mechanism which enables the animal organism, within 

 the space of a few days and with no apparent exertion, to synthesise a 

 series of new compounds of such extraoi'dinary complexity. 



The number of antibodies which are known is now very large 

 and is constantly increasing, but the above examples are probably 

 suflScient to give a general idea of the conditions under which 

 immunity reactions take place, and we may proceed at once to 

 consider the question of haemolysis with which we are more im- 

 mediately concerned. 



The study of haemolysis, thanks to the labours of Bordet, Ehrlich 

 and Morgenroth, and a host of other workers, has added greatly to our 

 knowledge of the phenomena of immunity, and haemolytic methods 

 now find their place in the routine work of most bacteriological 

 laboratories. The subject is unfortunately of very great complexity, 

 and its somewhat appalling nomenclature has hitherto not tended to 

 render it attractive to workers in other branches. The phenomena in 

 themselves are however simple, and by keeping to concrete cases and 

 avoiding as far as possible technical terms, are easily described. 



Supposing, for instance, a rabbit is injected with the red blood 

 corpuscles of the ox, it is found that the serum of the rabbit, which 

 before treatment had no action on ox corpuscles, acquires after a few 

 days the power of di.ssolving these corpuscles very rapidly, owing to 

 the formation of a haemolytic antibody or " haemolysin " in the serum. 

 We can show that the haemolytic action is actually due to the presence 

 of this haemolysin, by mixing some of this haemolytic serum and fresh 

 ox corpuscles and keeping the mixture at 0° C. overnight in the ice 

 safe and then centrifuging. At this temperature no haemolysis takes 

 place but the haemolysin is bound by the corpuscles, and is entirely 



Journ. of Gen. in 9 



