432 STUDIES IN IMMUNITY. 



NaCl or CaCl 2 . This salt increases the affinity of the particles in 

 the complex for one another. In like manner, the agglutination of 

 corpuscles with suspensions may be forced to appear even in a citrate 

 medium on the introduction of sufficient amounts of CaCl 2 ; and, 

 what is more, if we use a solution of 7 per cent saccharose instead of 

 0.85 per cent salt solution as a medium, we may produce an aggluti- 

 nation of barium sulphate with corpuscles, which is prevented by the 

 citrate, on the simple addition of NaCl. 



These experiments may all be repeated with other insoluble sub- 

 stances, as, for example, CaFl 2 and mastic. Both these substances 

 agglutinate washed red blood cells; the agglutination is prevented 

 either by stable colloids or by sodium citrate, and this failure in 

 agglutination is due to the fact that the adhesion of the insoluble 

 substance with the corpuscles fails to occur. In the place of the 

 complexes, CaFl 2 plus corpuscles, or mastic plus corpuscles, the 

 complexes, CaFl 2 plus stable colloid or mastic plus citrate, occur. 

 The addition of a salt like CaCl 2 or NaCl causes the agglutination, 

 which has been inhibited by the citrate, to appear, just as it provokes 

 the agglutination of the corpuscles by barium sulphate in a citrate 

 medium.* 



* We have shown in Section II the inhibiting effect of sodium citrate on pre- 

 cipitation of fuchsin by alum. With every reserve as to the interpretation of this 

 fact we have, nevertheless, insisted on the analogy which seems to exist between 

 the function of the citrate in this instance and its action with suspensions. It is 

 with a similar reserve that we mention the effect of the citrate on otlver pheno- 

 mena of agglutination produced by alum. As we already know, Malvoz (Annales 

 de 1'Institut Pasteur, 1897) has shown that various chemical substances aggluti- 

 nate emulsions of bacteria. Alum agglutinates typhoid bacilli well; we have also 

 found that it agglutinates red blood cells and even dissolves them when a sufficient 

 dose is employed. All these phenomena fail to occur when even a small amount 

 of sodium citrate is present. Not only does agglutination fail to appear, but we 

 have been able to show that the citrate prevents the adsorption of the alum by 

 the bacteria or the red blood cells, which normally occurs when citrate is not pre- 

 sent. We have also found that bacteria that have been agglutinated by moderate 

 doses of alum, and then washed in distilled water, are well agglutinated on the 

 addition of NaCl (this fact may be compared with the agglutination of bacteria 

 by specific sera and with the observations of Beckhold (Zeitschrift fiir phys. 

 Chem., Vol. 48) on the flocculation of bacteria by the salts of heavy metals). If 

 we treat bacteria which have been mixed with alum in a citrated medium in the 

 same way, the subsequent agglutination by NaCl fails to occur. It is evident, 

 then, that the mode of action of the citrate in this instance seems comparable to its 

 action on substances in aqueous suspensions (barium sulphate, calcium fluoride or 

 mastic); but, owing to the fact that chemical reactions may take place between 

 alum and citrate, and thus prevent the manifestations produced by the alum, we 

 think it better to reserve any interpretation of this fact. 



