378 COLLECTED STUDIES IX IMMUNITY. 



the coagulin obtained by testing rabbits with human serum precipitates only 

 human serum and the serum of the nearest related species, apes. This reaction, 

 which was developed especially by the researches of Uhlenhuth and of Wasser- 

 mann, was therefore proposed for the forensic identification of blood. 



From this we see that, entirely in harmony with my views, the 

 injection of foodstuffs is followed by the production of typical anti- 

 bodies, which combine with the exciting agent in a specific manner. 

 An analogous reaction takes place in the normal processes of cell 

 nutrition and serves as the chief source of the protective substances 

 present in normal blood in such great numbers. 



The conditions become much more complicated than those just 

 described if, instead of the relatively simple soluble metabolic prod- 

 ucts, living cell material is employed. This is the case, for instance, 

 in immunization against cholera, typhoid, anthrax, erysipelas of swine, 

 and many other infectious diseases. 



In these diseases under certain circumstances there develop many 

 other reactive products beside the antitoxins produced against the 

 bacterial toxins. The reason for this is that every bacterium is a 

 highly complex living cell which, when it disintegrates in the animal 

 body, gives rise to a large number of different components. Of these 

 a great many are able to produce antibodies. 



Hence as a result of the introduction of bacterial cultures, in 

 addition to the specific bacteriolysins, which cause a solution of the 

 bacteria, we see substances develop, such as the antiferments 

 (v. Dungern, Morgenroth, Briot), the much discussed agglutinms 

 (Gruber, Durham, Pfeiffer), and the coagulins (Kraus, Bordet), 

 which specifically precipitate certain albuminous substances that 

 have passed into the culture fluid. 



The most interesting and important of the substances arising in 

 such an immunization are undoubtedly the bacteriolysins, which 

 have been studied especially by Pfeiffer and Bordet. At first it is 

 highly surprising that the injection of cholera vibrios into the animal 

 body should be followed by the formation of a substance which is 

 able to dissolve the cholera vibrio, and only thii> bacterium. This 

 action is so perfectly adapted to the purpose and is apparently so 

 novel that it seems to fall beyond the pule of the normal functions 

 of the body. It was therefore of the highest importance to explain, 

 from the standpoint of fellular physiology, the origin of these sub- 

 stances also. The solution of this problem offered considerable diffi- 



