422 BLOOD AND LYMPH. 



known that the serum of one animal may destroy the red corpuscles 

 of another animal. Thus, rabbits' blood corpuscles added to the 

 clear serum of a dog, cat, or man are quickly destroyed, with the 

 liberation of their hemoglobin. This action was formerly described 

 under the term "globulicidal action of serum," and was compared 

 to the similar destructive (bactericidal) action, exhibited by serum 

 toward some bacteria. In more recent literature the term hemol- 

 ysis has replaced that of " globulicidal action," and the hemolytic 

 effect that a serum may exert upon foreign corpuscles is attributed 

 to the presence in it of certain substances which in general are classed 

 as hemolysins. This hemolytic action is not due to a simple differ- 

 ence in osmotic pressure. The serums of the different mammalia 

 have all approximately the same osmotic pressure; the differences 

 are too slight to explain the effects observed. Moreover, if the 

 serum used is heated to 55° C. its hemolytic action is destroyed, 

 although no noticeable change occurs in the osmotic pressure. In 

 addition to the hemolysins found normally in the blood of different 

 animals it was shown first by Bordet * that they may be produced 

 artificially. The serum of guinea pigs has httle or no effect normally 

 on the red corpuscles of rabbits' blood. If, however, one injects 

 some rabV)its' blood beneath the skin of a guinea-pig and, if npops- 

 sary, repeats the process it will be found that the blood of this 

 particular guinea pig has now a strong hemolytic action toward the 

 red corpuscles of rabbits. This method of producing specific 

 hemolysins by means of subcutaneous or intraperitoneal injections 

 of foreign red corpuscles is designated as a process of immunizing, 

 and the serum of the animal in which a specific hemolysin has been 

 thus produced is frequently called, for convenience, an immune 

 serum. These terms are employed on account of the essential 

 similarity of the processes involved to those underlying the devel- 

 opment of immunity toward special diseases. When the body is in- 

 vaded by pathogenic bacteria the toxic substances produced by these 

 organisms stimulate the tissues to form specific antitoxins which 

 are capable of neutralizing the action of the bacterial toxins. The 

 body is thus rendered immune toward special bacteria, and that the 

 blood of the immunized animal actually contains a definite anti- 

 toxin may be shown in some cases by the fact that when injected 

 into another individual the latter also acquires the specific immun- 

 ity. So in regard to the hemolysins. The presence of the foreign 

 red corpuscles causes the development of a specific antibody 

 capable of destroying the special form of red corpuscle injected. 

 The substance in the red corpuscles which stimulates the tissue to 

 form an antibody is designated in general, according to the nomen- 

 clature of the day, as an antigen. Experiments indicate that the 



* Bordet, "Annales de I'lnst. Pasteur," 1895. 



