THE MECHANISM OF AGGLUTINATION. 151 



The fact that Dineur has reported is exact, but its interpretation 

 does not seem to be so. As a matter of fact, the favorable effect 

 of motion may also be noted in the formation of flecks in inert 

 inorganic precipitates. If a drop of serum is added to 5 or 6 c.c. 

 of a 0.7 per cent salt solution and nitric acid then added, an albu- 

 minous opacity is formed which, if left alone, clumps very slowly. 

 But if, when the precipitate has been formed, a small amount of the 

 fluid is poured into another tube and this tube held almost horizon- 

 tally and gently agitated, the precipitate is agglutinated in a few 

 moments in small white masses which float in a clear fluid. The 

 fluid which has been left standing, however, remains homogeneous 

 for a long time and the contrast between the two is very striking. 

 The same experiment may be performed with other albuminous 

 precipitates, as, for example, with a precipitate formed by nitric 

 acid in whey. The phenomenon to which Dineur attaches so much 

 importance is also distinctly visible when milk is agglutinated by 

 its specific serum. Dineur's observation, then, instead of pleading 

 for Gruber's theory offers a still further analogy between the agglu- 

 tination of bacteria and of inorganic particles. But there is another 

 still more significant analogy. 



We know that the collection of precipitates is frequently con- 

 trolled by such apparently insignificant causes as the presence of 

 salts in solution in the fluid. A clear example of this is offered 

 by clay, which forms a very fine and homogeneous emulsion in 

 distilled water, but clumps and falls rapidly in the tube if 

 placed in water containing sodium chloride. If we believe, then, 

 that the agglutination of bacteria depends on laws of molecular 

 adhesion, we might suppose that salts would have some effect on 

 this phenonenon as well; and such indeed proves to be the case. 

 Several 24-hour cultures of the cholera vibrio are suspended in 

 salt solution (10 c.c. to a culture) and to the homogeneous emulsion 

 obtained in this manner is added a powerful agglutinating dose of 

 cholera serum. The bacteria soon form flecks which fall to the 

 bottom of the tube. The tube is centrifugalized, the supernatant 

 fluid removed, and a compact mass of agglutinated bacteria left 

 in the bottom of the tube. These bacteria are then suspended in 

 water so as to form a rather thick emulsion, which is divided 

 in two equal parts and placed in two separate tubes. To the first 



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