CHAPTER IX 



THE PHENOMENON OF AGGLUTINATION 



WHEN bacteria are added to homologous immune serum there 

 occurs a peculiar agglomeration of the individual micro-organisms 

 into small clumps. The phenomenon is so general and so easily 

 observed that it is not surprising that it was noticed and reported by 

 a number of workers during the period of active investigation upon 

 serum reactions which preceded and followed the discovery of the 

 Pfeiffer phenomenon. Thus, in the years from 1891 to 1895, 

 Metchnikoff, 1 Charrin and Roger, 2 Isaeff and Ivanoff, 3 Washburn, 4 

 and several other workers made this observation with a variety of 

 bacteria and immune sera. But all of these observers failed to follow 

 up or analyze the process they incidentally noticed in the course of 

 other investigations. A thorough study of the phenomenon was not 

 made until 1896, when Gruber and Durham, 5 in Vienna, in the 

 course of their studies upon bacteriolytic reactions with colon bacilli 

 and cholera spirilla, again noticed the agglutination of these bacteria 

 in homologous immune sera, recognized the specificity of the reaction, 

 and called attention to its apparent independence of other previously 

 studied serum phenomena. 



The process known as agglutination consists in the following 

 train of occurrences. If we add to an even emulsion of bacteria a 

 small amount of homologous immune serum the micro-organisms 

 may be seen to collect rapidly in groups or masses, with a resultant 

 clearing of the fluid in which they have been suspended. The clumps 

 of bacteria gather in flakes which, not unlike flakes of snow, 

 sink to the bottom of the test tube. The speed and completeness 

 with which this phenomenon occurs depend, as we shall see, 

 upon the agglutinating strength and other qualities of the serum 

 which is employed, but the essential process of clumping is alike 

 in all cases. 



There are a' large number of different methods by which this 



1 Metchnikoff. Ann. de I'lnst. Past., 1892. 



2 Charrin and Roger. C. E. de la Soc. de Biol, 1889. 



3 Isaeff and Ivanoff. Zeitschr. f. Hyg., Vol. 17, 1894. 



4 Washburn. Journ. of Path, and Bact., 1896, p. 228. 

 6 Gruber and Durham. Munch, med. Woch., 1896. 



