CHAPTER XXVI 



AGGLUTINATION 



History. In 1889 Charin and Roger in studying the action of the 

 serum of sick and immunized animals on homologous bacteria, 

 observed that the Bacillus pyocyaneus behaved peculiarly when placed 

 in the serum of an animal immunized to this organism. In the serum 

 of a normal rabbit, this bacillus grows as it does in beef-tea, form- 

 ing an opaque culture, while in the serum of an animal immunized to 

 it, it forms floccules which soon subside leaving a clear supernatant 

 fluid. Two years later, Metschnikoff noticed that the vibrio which 

 bears his name behaves in a similar manner. He recorded this obser- 

 vation as follows: 



In the blood and serum of non-vaccinated guinea-pigs, the vibrio develops 

 as it does in ordinary liquid media, the individual organisms retaining their 

 motility and remaining distinct, one from the other. On the other hand, in 

 the blood and serum of vaccinated animals the vibrios become immobile, and 

 form smaller or larger floccules which float in the liquid. 



In 1893 Issaeff, and later he and Ivanoff observed the same phe- 

 nomenon and described it as follows : 



In the blood serum of healthy, non-immunized guinea-pigs the vibrio develops 

 rapidly, and after from four to five hours at 37 there is a uniform cloudiness 

 throughout the fluid, while the surface is covered with a scum; but in immune 

 serum, the microbes sink to the bottom of the tube, while the supernatant fluid 

 remains clear. This condition continues for from eight to nine days, and it 

 is not until the tenth day that the culture becomes cloudy and a scum appears 

 on the surface. 



These observations attracted no attention and in all probability their 

 significance was not appreciated by the observers themselves. In 

 1896, Gruber and Durham ascertained that this reaction is specific. 

 Each bacterium is clumped by the serum of animals which have been 

 inoculated with it and not by other sera. They suggested that the 

 phenomenon be designated as "agglutination" and that it would prove 



