CHAPTER VIII 

 THE AGGLUTININS 



AN exceedingly interesting and important group of antibodies, 

 which were discovered by Gruber and Durham in 1896 (though 

 their effect had been observed by Charrin and Roger in 1889 

 in the case of B. pyocyaneus), 1 are called the agglutinins, since 

 they have the power of agglutinating their antigens, or causing 

 them to adhere in masses. Their effect is best seen after the 

 addition of the serum of a patient convalescent from typhoid fever 

 (or of an animal which has been injected with typhoid bacilli) 

 to a living culture of the organism. The bacilli, which at first are 

 actively motile and are distributed uniformly throughout the fluid, 

 first lose their motility, and then individuals may be seen to move 

 nearer and nearer to one another, until they come into close contact. 

 It often happens, especially in weakly agglutinating sera, that this 

 approach of two bacilli may be seen to occur before their paralysis 

 has taken place. They then revolve rapidly round a common 

 axis, giving the observer the impression that they are united 

 together by a sort of invisible link, which they struggle to break. 

 This process continues, and fresh individuals are attracted to the 

 groups, until at last all the bacilli, instead of being scattered equally 

 throughout the fluid, are collected into masses, the intervening 

 fluid being free. The process may also be watched with the naked 

 eye, and the emulsion, which is at first uniformly turbid, will be 

 seen to lose its homogeneity, and take on a finely granular 

 appearance. This at first can only be realized by comparison 

 with a control specimen to which no serum has been added, but 

 in a little time it will be obvious that flocculi of bacilli are being 

 formed, and that between these flocculi the fluid is clearing. Soon 



1 The effect had also been observed by Metchnikoff in the case of V. Metchni- 

 kovi in 1891 ; he was inclined to regard it as a general phenomenon, but failed 

 to find it in another case. Similar appearances had also been seen by Issaeff 

 in 1893. 



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