374 BIOLOGY OF PNEUMOCOCCUS 



According- to Heidelberger and Kendall, an inhibition-zone effect 

 appears to be a chemical equilibrium which might be expressed by 



(3) AS 2 + S^±AS 3 



In equilibrium (1) the reaction tends to proceed strongly to the 

 right since AS is only slightly soluble. Reaction (2) will go far- 

 ther to completion and more AS 2 will be precipitated (since AS 2 

 has an appreciable solubility and dissociation tendency) when a 

 little S is added after equilibrium (2) has been reached. When 

 much S is added, equilibrium (3) comes into play and the precipi- 

 tate dissolves. The authors suggested as an analogy the reaction 

 between silver and the cyanide ion, where a small amount of CN" 

 causes a precipitate of AgCN, and an excess of CN" causes the 

 formation of the silver cyanide complex which is soluble. 



Heidelberger, Sia, and Kendall (1930) 630 described a rapid and 

 simple method for the approximate determination of the specifi- 

 cally precipitable protein in Type I antipneumococcic serum. In- 

 asmuch as a close parallel was found to exist between the amount 

 of specifically precipitable protein and the number of mouse pro- 

 tection units, and because of the rapidity, simplicity, and economy 

 of the method, the authors proposed its use instead of the mouse 

 protection test as a basis for the titration of standard serum and 

 for the comparison of other serums with the standard. 



Heidelberger and Kendall (1932) 619 devised a method, based on 

 the precipitin reaction, for the microdetermination of the spe- 

 cific polysaccharide of Type III Pneumococcus. By the method, 

 as little as 0.01 milligram of Type III polysaccharide could be 

 measured, while the procedure appeared to be applicable to any 

 specific polysaccharide upon standardization of an homologous 

 antiserum or antibody solution in the region of excess antibody. 

 In another paper, 620 the authors described precipitin reactions 

 performed with partial hydrolytic products of the specific cap- 

 sular polysaccharide of Type III Pneumococcus freed quantita- 

 tively from unhydrolyzed specific polysaccharide. The fractions 



