424 BLOOD AND LYMPH. 



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 little or no effect normally 

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

 some rabbits' blood beneath the skin of a guinea-pig and, if neces- 

 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 

 antigen in the red corpuscles is not the hemoglobin, but rather some 

 constituent of the stroma. This interesting reaction may be 

 obtained with other cells than the red corpuscles and bacteria. By 

 injecting spermatozoa, an antibody may be produced in the blood 

 which destroys this particular form of cell, and the same fact holds 

 good for epithelial cells, etc. Moreover, solutions of foreign proteins 

 injected in the same way give rise to the formation of definite anti- 

 bodies capable of coagulating or precipitating the special proteins 

 used. In this last case the antisubstance is designated as a 

 precipitin on account of its precipitating effect on the solution 

 of protein (see Appendix, p. 1011). This wonderful protective 

 adaptation of the body toward the invasion of foreign cells 

 or proteins is at bottom doubtless a chemical reaction dependent 

 upon the properties of the living cells, but the nature of the proc- 

 esses involved is not at all understood, and the phenomenon is, 

 * Bordet "Annales de 1'Inst. Pasteur," 1895. 



