200 INFECTION AND IMMUNITY 



This process he observed microscopically by abstracting, from time 

 to time, a small quantity of the peritoneal exudate and studying it in 

 hanging-drop preparations. The reaction was specific in that the de- 

 structive process took place to any marked extent only in the case of the 

 bacteria employed in the immunization. 



Metchnikoff ,' Bordet, and others not only confirmed Pfeiffer's obser- 

 vation, but were able to show that the lytic process would take place 

 in vitro, as well as in the animal body. The existence of a specific 

 destructive process in immune serum was thus established for the vibrio 

 of cholera and soon extended to other microorganisms. The constitu- 

 ents of the blood serum which gave rise to this destructive phenomenon 

 were spoken of as bacteriolysins. 



Following closely upon the heels of Pfeiffer's observation came the 

 discovery of another specific property of immune serum by Gruber and 

 Durham.^ These workers noticed that certain bacteria, when brought 

 into contact with the serum of an animal immunized against them, 

 were clumped together, deprived of motility, and finnly agglutinated. 

 They spoke of the phenomenon as agglutination and of the substances 

 in the serum giving rise to it as agglutinins. 



The list of antibodies was again enlarged by Kraus,^ who in 1897 

 showed that precipitates were formed when filtrates of cultures of 

 cholera, typhoid, and plague bacilli were mixed with their specific 

 immune sera. He called the substances which bestowed this property 

 upon the sera precipitins. 



The treatment of the animal body, therefore, with bacteria or their 

 products gives rise to a variety of reactions which result in the presence 

 of the " antibodies " described above. Extensive investigation has shown, 

 however, that the power of stimulating antibody production is a phe- 

 nomenon not limited to bacteria and their products alone. Antitoxins, 

 we have already seen, may be produced with a variety of poisons of 

 plant and animal origin. Lysins, agglutinins, and precipitins, likewise, 

 may be produced by the use of a large number of different substances. 

 Chief among these, because of the great aid they have given to the theo- 

 retical investigation of the phenomena of immunity, are the red blood 

 cells. Bordet ^ and, independently of him, Belfanti and Garbone ^ showed 



^ Metchnikoff, Ann. de I'inst. Pasteur, 1895. 



^ Gruber und Durham, Munch, med. Woch., 1896. 



^ Kraus, R., Wien. Win. Woch., 32, 1897. 



* Bordet, Ann. de I'inst. Pasteur, 1898. 



' Belfanti et Carbone, Giornale della R. Acad, di Torino, July, 1898. 



