130 Immunity 



The injection of the precipitinogenic serum into animals 

 results in the formation of anti-precipitins by which their 

 activity is neutralized. 



II. Agglutination. This phenomenon was first observed 

 by Charrin and Roger* in the course of some experiments 

 with Bacillus pyocyaneus. They found that the bacilli 

 when introduced into serum of animals infected with or 

 immunized against cultures of Bacillus pyocyaneus ceased 

 their active movements, became aggregated in clusters and 

 settled to the bottom, leaving the fluid clear. Observations 

 confirming and enlarging upon the observation were made 

 by MetschnikofT, f IssaeffJ and others. Gruber and Durham 

 made an elaborate and now classic study of the subject, first 

 employing the term "agglutination" to the phenomenon, 

 and " agglutinins" to the substances in the serum by which 

 it might be brought about. They found that when cholera 

 or typhoid bacilli are mixed with their respective immune 

 serums, the organisms lose motility and become aggregated 

 in clusters, masses or "clumps." They further showed 

 the reaction to be specific within certain limitations, i. e., 

 typhoid immune serum agglutinated typhoid-like bacilli 

 but no others, etc., and they saw in the phenomenon a 

 practical means for the differentiation of different, closely 

 related bacteria, an application that has, indeed, become a 

 useful one. 



It remained for Widal|| to show that it had a much more 

 important application, in that the micro-organism being 

 known, the effect produced by a serum upon it would be an 

 indication of the past infection of the animal from which 

 the serum was secured. The first practical application was 

 made in connection with typhoid fever, and the brilliant 

 success attending it had led to the test being known as the 

 "Widal reaction" (q.v.). 



The agglutinins are stable substances that resist drying 

 and can be kept dry and active for years. Widal and Sicard 

 found that they pass with difficulty through a porcelain 

 filter and do not dialyze. They are precipitated in part by 

 15 per cent, of sodium chloride that throws down fibrinogen 



* "Compte rendu de la Soc. de Biol.," 1899, p. 667. 



t "Ann. de 1'Inst. Pasteur," v. 1891. 



t Ibid., vn, 1893. 



" Munchener med. Woch," 1896, No. 9. 



|| "Soci^te" Medicale des Hopitaux," June 26, 1896. 



