668 LECTURE XXIX. 



that we are now only constructing as it were a scaffolding which will per- 

 haps serve to lead future investigation into definite channels. 



We are not alone in this idea. Franz Hamburger, 1 starting from entirely 

 different experimental results, has likewise traced in a most interesting 

 manner the individuality of a species and its maintenance to a definite 

 composition of the cells and body fluids. This idea is closely related to the 

 so-called biological reaction, which we shall discuss briefly. Its discovery 

 is associated with the names of Bordet, Tchistowitsch, and Nolf. 2 It rep- 

 resents merely a generalization of the Law of Immunity, and depends upon 

 the formation of very specific substances after the introduction of products 

 foreign to the species. The knowledge of this principle is of great signifi- 

 cance for the further development of physiological chemistry. It forms a 

 bridge to the domain of pathology; and we become more and more con- 

 vinced that pathological processes are not sharply distinct from physio- 

 logical ones, but are common manifestations of body cells under definite 

 conditions. The limitations of purely physiological-chemical investiga- 

 tion are thus being more and more eliminated. By the improvement of 

 methods, it continually enters new fields, and on the other hand other 

 fields constantly attach themselves to it, and await new impulses for 

 further fruitful work. Here we must introduce the name of an investigator 

 to whom, more than any one else, our thanks are due for the expression 

 of this unity between physiological and pathological processes, namely, 

 Paul Ehrlich. We shall return to his theory, which has served as a founda- 

 tion for important investigations in this domain. In this connection also 

 we must call attention to the great importance of Pawlow's work. 3 He 

 likewise clearly recognized the numerous transition stages between physio- 

 logical and pathological processes, from his observations on the functions 

 of the alimentary tract under varying conditions. 



It is quite out of the question for us to give here even a brief summary 

 of all the investigations which are based upon the conception of the "bio- 

 logical reaction." In a very short time it has developed into an important, 

 independent branch of biological science. We shall here very briefly call 

 attention to a few fundamental experiments. If we inject, for example, 

 horse-blood into a rabbit, the serum of this animal soon shows characteristic 

 new properties towards the injected blood. It dissolves the blood-corpuscles 

 and forms a precipitate with the new serum, called the precipitin-formation. 

 This reaction is a specific one. The serum of the rabbit which has been 



1 Loc. cit. 



2 Jules Bordet: Annales de ITnstitute Pasteur, 1899, 240. Tchistowitsch: Ibid. 

 1899, 413. Nolf: Ibid. 1900, 299. Cf. Rostoski: Zur Kenntnis der Prazipitine. Wiirz- 

 burg, 1902. 



3 Pawlow-Walther: Das Experiment als zeitgemasse und einheitliche Methode medi- 

 zinischer Forschung. Bergmann, Wiesbaden, 1900. 



