GENERAL PROPERTIES! THE CORPUSCLES. 399 



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 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 antisubstance 

 capable of destroying the special form of red corpuscle injected. This 

 interesting reaction may be obtained with other cells than the red 

 corpuscles and bacteria. By injecting spermatozoa a toxin or lysin 

 may be produced in the blood which destroys this particular form 

 of cell, and the same fact holds good for epithelial cells, etc. More- 

 over, solutions of foreign proteins injected in the same way give rise 

 to the formation of definite antisubstances capable of coagulating or 

 precipitating the special proteins used. In this last case the anti- 

 substance is designated as a precipitin on account of its precipita- 

 ting effect on the solution of protein (see Appendix, p. 909). 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 processes involved is not at all understood, and the phenomenon 

 is, therefore, designated provisionally as a biological reaction. The 

 specific hemolysins produced by immunization have been studied 

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



