120 



Scientific Proceedings (52). 



embryos are not injured by the lecithin, however, as they will 

 ultimately develop to normal plutei if left in these solutions for a 

 sufficient time. 



If cholesterin, suspended in a mixture of m/100 sodium oleate 

 and m/2 NaCl be mixed with the lecithin in equal proportions 

 the retarding action of the lecithin upon the development of 

 purpuratus eggs is almost completely neutralized. The slight 

 retardation which is observed in these mixtures may be due to 

 the sodium oleate which is employed to keep the cholesterin in 

 suspension, since sodium oleate is very toxic for sea-urchin eggs 

 and embryos. 



Cholesterin itself, when added to sea-water, has no influence 

 upon the rate of development of the eggs. The emulsions of 

 cholesterin are, however, coagulated by the salts in sea-water 

 and the cholesterin is completely thrown out of suspension in the 

 form of coarse flocculi. 



79 (775) 



On acid agglutination as a method of differentiation of bacteria. 



By H. J. Sears. 



[Division of Bacteriology, Department of Medicine, Stanford 



University.] 



Michaelis and several other workers following him have claimed 

 for the phenomenon of acid agglutination a specificity comparable 

 with that of specific serum agglutination. The reaction is specific, 

 they say, in that optimum agglutination is produced in suspensions 

 of bacteria of a single species by a definite concentration of 

 hydrogen ions, irrespective of the acid used, and in that this 

 concentration is, in general, different for different species. Their 

 method has been to prepare solutions of definite hydrogen ion 

 concentrations by using mixtures of a weak acid with its sodium 

 salt, the concentrations being calculated from the formula 



, C ac id 



C H = k- ~ , 



'-salt 



where k represents the dissociation constant of the acid used. 

 The differences between the constants obtained in this way for 



