504 EXPERIMENT STATION RECORD. 



The double picrate of creatinin and potassium was also prepared from urine 

 in the manner described. The readings obtained with this material were like- 

 wise satisfactoi-y. Both salts were found to be very sensitive to the amount 

 of alkali used in the method. 



The reaction between metallic salts and the soluble carbonates, and its 

 bearing upon the precipitation of protein, W. N. Heard (Jour. Physiol., 4S 

 (1913), No. 2, pp. 104-128, figs. 3). — "Since thorough dialysis removes all 

 precipitation of emulsoid protein by salts of the heavy metals, except in con- 

 centrated solutions of the latter, precipitation must be intimately associated 

 with some removable constituent. The experiment of adding salts to such 

 dialyzed solutions shows that the production of a body with a very low solu- 

 bility product is the necessary condition in causing precipitation. The only 

 salt found in the dialyzate which is capable of producing this result is a bicar- 

 bonate (except in the case of silver). The reaction of the metals with emulsoid 

 protein closely follows the reaction of these metals with soluble bicarbonates, 

 and it is therefore concluded that the process depends upon this reaction. 



" If it be considered to be proved that the presence of soluble bicarbonates 

 is the determining factor in the precipitation of emulsoid protein, it establishes 

 a probability that the precipitation of suspensoid protein is due to a reaction 

 between the metals and soluble carbonates. The reaction between the metals 

 and suspensoid protein follows in degree and also in the shape of the curves 

 produced, the reaction between these metals and soluble carbonates, the general 

 increase of precipitability accompanying the suspensoid state coupled with the 

 partial conversion at any rate of the bicarbonate into carbonate being suggested 

 as the cause of the difference of behavior of the two kinds of protein with the 

 salts of the metals. No dialysis can remove all the salts present and it can 

 easily be shown that a protein solution after suthcieut dialysis to make it non- 

 precipitable, as above stated, is distinctly alk.-iline to alizarin and when con- 

 verted into the suspensoid state requires a certain definite quantity of acid to 

 neutralize it, the amount being about one-quarter of that which would be needed 

 with it undialyzed. 



" Probably the precipitation of bicarbonates and carbonates acts mainly by 

 the removal of the OH ions freed by the hydrolysis of these salts. But the 

 results with AgNOa and NaCl suggest that there are other factors." 



Quantitative determination of peptic activity, S. von Boguandy (Hoppe- 

 8ci/lcr''s Ztschr. Physiol. Chem., 8Jf (1913), No. 1, pp. 18-28; abs. in Ghent. A&s., 

 7 (1913), No. 13, p. 2235). — From the Schiitz (polarization) and Volhard 

 methods for determining peptic activity a method was evolved which combines 

 some of the salient features of the two. The casein used in the experiments 

 contained 7.3 per cent of water, and the dried material 1.08 per cent of ash 

 and 15.34 per cent of nitrogen. 



The solutions required in the test were as follows : A 3.3 per cent solution of 

 casein is prepared by stirring up 17.5 gm. of casein with 250 to 300 cc. of dis- 

 tilled water and then adding 27.5 cc. of noi-mal hydrochloric acid solution ; the 

 solution is then poured into a 500 cc. flask and filled up to the mark with water. 

 The solution of the casein is accomplished in the water bath at 40° C. and 

 requires from J to 1 hour. As a precipitating reagent for the casein a solution 

 composed of 150 gm. of sodium sulphate, 50 gm. of magnesium sulphate. 100 cc. 

 of alcohol (96 per cent), and water to make 1 liter is employed. If crystals 

 are deposited in the solution they can easily be dissolved by heating the solu- 

 tion to a temperature of from 35 to 40". 



The actual procedure is as follows: In a 100 cc. graduated flask place CO cc. 

 of the casein solution and the necessary amount of Griibler's pepsin in 0.2 per 

 cent hydrochloric acid, and then place the flask in a water bath kept at 40°. 



