AGGLUTININS 47 



bacteria which lasts a short time and is followed 

 by a gradual formation of clumps. One gets the 

 impression that the bacteria are dying together. 

 Frequently one sees bacteria which have recently 

 joined a group make violent motions as though they 

 were attempting to tear themselves away; then 

 they gradually lose their motility completely. Even 

 the larger groups of bacteria may exhibit movement 

 as a whole. After not more than one or two hours 

 the reaction is completed; in place of the bacteria 

 moving quickly across the field, one sees one 01* 

 several groups of absolutely immobile bacilli. Now 

 and then in a number of preparations one sees 

 a few separate bacteria still moving about among 

 the groups. If the reaction is feeble, either because 

 the immune serum has been strongly diluted or 

 because it contains very little agglutinin, the groups 

 are small and one finds comparatively many iso- 

 lated and perhaps also moving bacteria. It is 

 essential each time to make a control test of the 

 same bacterial culture withoxit the addition of 

 serum. Under some circumstances the reaction 

 proceeds with extraordinary rapidity so that the 

 bacilli are clumped almost immediately. By the 

 time the microscopical slide has been prepared 

 and brought into view nothing is to be seen 

 of any moving or isolated bacteria, and only by 

 means of the. control test is it possible to tell 

 whether the culture possessed normal motility. 



