G. McGUIRE AND K, G. FALK 219 



the former. The residues after removal of the juice showed moisture 

 contents of between 60 and 70 per cent when dried at 100°. The 

 juice as obtained contained on an average between 3 and 4 mg. of 

 nitrogen per cc. for new potatoes, and somewhat more, 4 to 5 mg., 

 for winter and sprouted potatoes. 



The hydrogen ion concentration of the juice as prepared was very- 

 close to 10"'' N or pH 6.0 in every case.^ 



Although the properties of the juice from different lots of potatoes 

 varied somewhat, an attempt was made to make each experiment as 

 complete as possible by running all the necessary blanks. The actions 

 found, therefore, should have general validity. It may also be stated 

 that duplicate determinations agreed satisfactorily. 



The results of the actions of the enzymes in the juice upon the con- 

 stituents of the juice itself and upon added soluble starch solution 

 are given in Table I. The action on the added starch is taken as the 

 difference between the action obtained on the juice plus water and 

 that of the juice plus starch. The results are given as mg. of cuprous 

 oxide obtained by the reducing actions of 15 cc. portions of the solu- 

 tions. The juice itself was found to have a pH value of 6.0, and the 

 solutions of different acidities were made up by the addition of small 

 quantities of different strengths of acid or alkali. This prevented 

 undue dilution and made the results practically comparable without 

 further calculation. The values of the reductions obtained were 

 corrected for blanks, so that the table shows the actual amount of 

 CU2O corresponding to the reducing substances formed during incu- 

 bation due to the enzyme actions. For the fresh juice the blanks 

 ranged in the extreme cases between 100 and 200 mg. of CU2O. 

 The enzyme actions did not appear to depend directly on the re- 

 ducing actions of the juice although it seemed in a number of exper- 

 iments as if, as with the cabbage, carrot, yellow turnip, and white 

 turnip amylases, the greater the blanks (on the fresh juice) the 

 greater were the actions. 



There were considerable variations in the individual experiments, 

 but the large number of determinations made should make it possible 

 to obtain satisfactory mean values. The figures in parentheses in 

 Table I give the mean values for the separate preceding figures. 



^ Cohn, E. J., Gross, J., and Johnson, 0. C, /. Gen. Physiol., 1919-20, ii, 145. 



