PRECIPITINSPRECIPITINOIDS 149 



concentrations of agglutinins in immune sera, as measured by present- 

 day methods, throws no light upon the degree of immunity or the 

 prognosis. Very severe typhoid infections, for example, may show 

 little agglutinin in their sera, and mild cases may exhibit sera com- 

 paratively rich in agglutinin content. Their chief value at the present 

 time lies in their relation to the diagnosis of disease. 



PRECIPITINS. PRECIPITINOIDS. 



In the preceding section it was shown that the sera of animals 

 immunized with various bacteria contained substances agglutinins 

 which agglutinated the specific organisms. Kraus 1 showed that 

 these immune sera would cause a precipitate when they were added 

 to clear filtrates of the specific organisms. During the process of 

 immunization, therefore, specific antibodies, termed precipitins, are 

 formed, which react with the specific soluble antigen, precipitinogen, 

 in germ-free filtrate of broth cultures of the specific organisms, to 

 form a precipitate. Later investigations have shown that any soluble 

 protein, as egg-albumen, injected into experimental animals may 

 stimulate the production of specific precipitins which will cause a 

 precipitation in clear solutions of the homologous protein. These 

 reactions have a marked specificity: The sera of animals immunized 

 against casein of cows' milk, for example, will cause precipitation in 

 clear solutions of this protein, but will fail to cause precipitation in 

 solutions of casein from human milk. The sera of closely-related ani- 

 mals may contain small amounts of "group" precipitins, and biological 

 relationships have been established, based upon the community of 

 these antibodies. Thus, the sera of certain anthropoid apes 2 are 

 said to be precipitated by the sera of animals immunized to the serum 

 of man; sera from the lower- monkeys fail to react with the human 

 serum. From these observations the inference has been drawn that 

 these anthropoid apes are more closely related to man than are the 

 lower monkeys. 3 



Precipitins closely resemble agglutinins in their method of formation, 

 their resistance to physical agents and their reactions. Like the 

 agglutinins, they possess both a thermostabile haptophore or combining 

 group and a thermolabile ergophore group. The precipitinophore 



1 Wien. klin. Wchnschr., 1897, 736. 



2 Griinbaum, Lancet, January, 1902. 



3 See Nuttall, Jour. Hyg., 1901, i, No. 3; Proc. Royal Acad., November, 1901, Ixix; 

 Proceedings Cambridge Philosophical Society, January, 1902; Brit. Med. Jour., April, 

 1902, i, for full details. 



