BY R. GREIG SMITH. 71 



tend to form upon small solid particles just as rain-drops gather 

 around dust particles, crystals form around string, and even 

 precipitates adhere to glass. Thus Kraus' precipitate forms upon 

 the flagella and upon the bacterial cell. It forms upon the 

 bacteria the more readily since the capsule is saturated with the 

 agglutinable substance which slowly oozes through the membrane. 

 But the building up of the molecular aggregates still proceeds, 

 and the precipitated films surrounding the bacteria are attracted 

 to one another, so that small clumps are formed and agglutination 

 is made manifest, because we can see the comparatively large 

 bacteria. The thin precipitated films elude our observation. 



Although the residual affinity alone has been used to explain 

 the phenomenon, yet the base of the flocculating salt over and 

 above its attraction for the loose water molecules plays a part in 

 combining with the molecular aggregates. The base partly 

 attracts the Avater molecules, and partly replaces them. Even 

 some of the acid radicles may in some instances be carried down 

 (attracted) with the precipitate as in the coagulation of slimes 

 and mucin bodies by salts in alcoholic solution. 



Agglutination is a chemical phenomenon, and the natural laws 

 which govern it are those which obtain in the precipitation of 

 chemical compounds, the coagulation of precipitates, the floccula- 

 tion of clay particles, and even the solution and diffusion of 

 substances in water. The bodies of the bacteria have tended to 

 obscure the mechanism of the process, a thing which should not 

 have been done in view of what Nicolle did when he agglutinated 

 particles of talc suspended in filtered typhoid cultures. 



A paper has recently been written by Harrison"^ upon the 

 agglutinating substance of typhoid bacteria. He took typhoid 

 bacteria which agglutinated readily with active sera, and treated 

 them with with pyocyanase, an enzyme which has the jDower of 

 dissolving the outer membranes of bacteria. After washing the 

 membraneless bacteria with water, he found that they were 

 not now capable of being agglutinated From this he concluded 



* Harrison, Cent. f. Bakt. 1 Abt. xxx., 115. 



