194 COLLOIDS IN BIOLOGY AND MEDICINE 



The bacteria are previously prepared for phagocytosis by certain 

 immune substances in the serum called opsonins. 



The study of these phenomena was very much simplified, when it 

 became possible to transfer many of them from the living organism 

 to test tubes. They were thus freed from disturbing epiphenomena 

 and made susceptible to quantitative investigations. By these 

 methods of study, we have learned a number of properties of the 

 blood and cells, which have no direct influence on the natural pro- 

 tection of the organism against the attacks of microorganisms, or 

 which may be regarded merely as epiphenomena. They lead to the 

 knowledge that the weapons of the organism against disease germs 

 are not teleologically forged for this sole purpose, but that they are 

 the product of a universal biologic law, according to which the 

 organism produces antisubstances against all kinds of substances 

 foreign to the species (art-fremde). 



In accordance with their historic recognition, and the method of 

 their investigation, it is customary to class them with immunity phe- 

 nomena: I am referring to the substances which dissolve and floccu- 

 late blood corpuscles, the hemolysins and hemagglutinins and the 

 albumin-precipitating substances, the precipitins: and finally the 

 Wassermann reaction in syphilis, and anaphylaxis. 



If the sera of two animals, e.g., cattle serum and rabbit serum, are 

 mixed, the solution remains clear. If an animal, e.g., a rabbit, is in- 

 jected with the serum from a different species of animal, e.g., cattle 

 serum, substances are formed in the rabbit, precipitins. 1 If we then 

 mix the serum of such an animal, "cattle-rabbit," with ox serum, a 

 precipitate forms. Agglutinins and hemolysins develop in a similar 

 way. If a rabbit has cattle blood corpuscles injected into its veins, 

 substances develop in the rabbit serum which agglutinate and dissolve 

 the cattle blood corpuscles. Hemolysin consists of two substances, 

 one heat resisting (thermostable) and specific, the amboceptor, and 

 another, heat sensitive (thermolabile, destroyed at 55 C.) and non- 

 specific, the complement. Only the amboceptor develops as a result 

 of injecting the red blood corpuscles, the complement is always 

 present in every serum. However, both are required for hemolysis. 

 We have now explained the formation of precipitins for cattle serum 

 or blood corpuscles in rabbits, but the principle is of general applica- 

 tion for the injection of blood into a different species of animals. To 



1 The so-called "precipitin reaction" is of great medico-legal importance. 

 It serves for the differentiation 01 human and animal blood, for which a small 

 drop suffices. It is also employed in detecting adulterations (horse-meat in 

 sausage, etc.). In the study of phylogenesis it is a valuable aid particularly in 

 teaching the natural relationships of animals. 



