GENERAL PHYSICAL AND CHEMICAL PROPERTIES 31 



When the corpuscles of one animal are injected intraperitoneally 

 or subcutaneously into an animal of a different kind, the serum of 

 the latter acquires the property of agglutinating and laking the 

 corpuscles of an animal of the same kind as that whose corpuscles 

 have been injected. This is especially marked if the injection is 

 several times repeated at intervals of a few days. If, for instance, 

 dog's corpuscles are injected into a rabbit, the rabbit's serum after 

 a time becomes strongly hsemolytic for dog's corpuscles. It also 

 agglutinates them. This is due to the appearance in the rabbit's 

 serum of an amboceptor and an agglutinin which have a specific 

 action on dog's corpuscles. Such a serum is often termed an 

 immune serum, and the animal which has received the injections 

 is spoken of as immunized in regard to this particular kind of 

 corpuscles. For the reaction involved in the production of the 

 amboceptor and agglutinin is a particular case of the peculiar and 

 specific response which the body makes to the presence of foreign 

 juices or cells, including bacteria, and which constitutes an attempt 

 to render itself ' immune ' to them. 



Many other animal cells besides the coloured blood-corpuscles give 

 rise, when injected, to similar specific substances (cytolysins), which 

 cause destruction of cells of the same kind e.g., leucocytes and 

 spermatozoa.* The process of haemolysis is more easily followed 

 than the cytolysis of ordinary cells. Yet in its main features it is 

 essentially similar. 



In each case the specific antibody seems to be produced in response 

 to the presence of some particular constituent of the foreign cell. The 

 substances which on injection give rise to antibodies are spoken of as 

 antigens. In the case of the erythrocytes there is evidence that the 

 antigens (both the haemolysinogen, which causes the production of 

 specific amboceptor, and the agglutininogen, the substance which gives 

 rise to specific agglutinin) are lipoids, or are so closely associated with 

 the lipoids of the corpuscles that they are extracted by the same solvents. 

 Thus ethereal extracts of erythrocytes cause the production of haemol- 

 ysin and agglutinin, just as the entire corpuscles do. The group of 

 antibodies known as precipitins is of special interest. 



Precipitins. When the serum of one animal is injected into 

 another of a different group, the serum of the latter acquires the 

 property of causing a precipitate in the normal serum of animals 

 of the same group as that whose serum was injected, but not 



* Recent studies have tended to modify the view that the cytotoxins 

 formed after the introduction of different foreign tissues into animals are 

 quite specific for each tissue. Thus Lambert, using tissues cultivated on 

 media outside of the body for testing the toxic action, finds that the plasma 

 of guinea-pigs which have received injections of either chick embryo heart or 

 intestine becomes toxic for both of these tissues. In like manner the plasma 

 of guinea-pigs treated by injection of rat sarcoma, a tumour which can be 

 propagated by inoculation in rats, acquires a toxic action on cultures of both 

 rat sarcoma and the skin of embryo rats. And the plasma of guinea-pigs 

 treated with rat embryo skin is also toxic for cells of both types. 



