122 Immunity 



practical medicolegal importance in recognizing blood-stains. 

 Nuttall comes to the following conclusions: 



"(i) The investigations we have made confirm and extend the observations 

 of others with regard to the formation of specific precipitins in theblood-serum 

 of animals treated with various sera. (2) These precipitins are specific, although 

 they may produce a slight reaction with the sera of allied animals. (3) The sub- 

 stance in serum which brings about the formation of a precipitin, as also the pre- 

 cipitin itself, are remarkably stable bodies. (4) The new test can be successfully 

 applied to a blood which has been mixed with those of several other animals. 

 (S) We have in this test the most delicate means hitherto discovered of detecting 

 and testing bloods, and consequently we may hope that it will be put to forensic 

 use." 



Further perfection in the technic of the precipitation experiments 

 can be found in a paper by Nuttall and Inchley,* 



The precipitinogen is capable of acting as an antigen and the 

 injection into animals of serum containing it results in the formation 

 of anti-precipitins. 



AGGLUTINATION 



/ 



Agglutination is a phenomenon of infection and immunity in 

 which the serum or other body juice of the infected animal so acts 

 upon the infecting micro-organism as to destroy its power of move- 

 ment, and cause it to sediment in clusters in the liquid in which it 

 is suspended. This phenomenon was first observed by Charrin 

 and Roger t in the course of experiments with Bacillus pyocyaneus. 

 They found that when bacillus pyocyaneus was introduced into a 

 test-tube containing the diluted serum of an animal infected with or 

 immunized against it, the bacilli ceased their active movements, 

 became aggregated in clusters and settled to the bottom of the tube, 

 leaving the supernatant fluid clear. Observations confirming and 

 enlarging upon the subject were made by Metschnikoff , J Issaeff§ 

 and others. Gruber and Durham || made an elaborate and now 

 classic study of the subject, first employing the term "agglutina- 

 tion" to the phenomenon, and "agglutinins" to the substances in 

 the serum by which it might be brought about. They foimd that 

 when cholera or typhoid bacilli are mixed with their respective 

 immune serums, the organisms lose motility and become aggre- 

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

 reaction to be specific within certain limitations, i.e., typhoid im- 

 mune serum agglutinated typhoid-like bacilli but no others, etc., 

 and they saw in the phenomenon a practical means for the dif- 

 ferentiation 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 



* "Journal of Hygiene," 1904, iv, p. 201. 

 f'Compte rendu de la Soc. de Biol.," iSgg, p. 667. 

 t "Ann. de I'lnst. Pasteur," 1891, v. 

 § Ibid., 1893, VII. 



I| "Miinchener med. Woch.," 1896, No. 9. 

 ** "Soci6t6 M^dicale des Hopitaux," June 26, 1896. 



