1923] 



JENNISON — POTATO BLACKLEG 47 



medium in which the microorganisms in question were grown 

 was determined by this method, as was the copper-reducing value 

 of control portions. Differences were carefully noted and 

 carbohydrate utilization estimated by reference to Shaffers table 



r-glucose equivalents, having first determined by cal- 



that 1 cc. of the N/20 permanganate is equivalent to 



mgms. copper. For the technique of the complete method 



of 



e under "Technique 



According to Plimmer ('15) pure lactose reduces Fehling 



m 



as strongly as glucose. These figures were employed in making 

 estimates of the amounts of these disaccharides consumed by 

 the microorganisms under consideration. It was assumed in this 

 work that the fructose and galactose used reduced Fehling's 

 quite as strongly as glucose. Certain dextrins reduce Fehling's 

 slightly, but the product which I employed did not; nor did 

 the saccharose and potato starch. Where it became necessary 

 to hydrolyze these last-named substances in order to determine 

 whether there had been utilization of the substance as such, the 

 following methods were used : 



Davis and Daish ('13) employed citric acid in pref- 

 erence to a mineral acid for inverting cane sugar. In dealing 

 with plant extracts, in which there was an accumulation of so- 

 dium acetate, they employed 10 per cent citric acid. 



Method.— (1) Make solution faintly acid to 



by addition of a few_ drops of concentrated H 2 S0 4 ; (2) add 



minutes 



Sucro 



me 



by weight of citric acid; (3) 



pounds pressure, cool, and neutralize to phenolphthalein 



NaOH 



Starch and dextrin. Method.— (I) To a 1 per cent starch 



water; (2) 



) add 0.3-0.5 cc. cone. HC1 and 10 cc. distilled 



minutes 



sure; (3) cool, neutralize to phenolphthalein with NaOH, and 

 estimate as glucose. The amount of glucose times 0.9 equals 

 the weight of starch hydrolyzed. 



Maltose and lactose. Method.— (1) To 10 cc. of a 1 per cent 

 solution of the sugar add 0.3-0.5 cc. cone. HC1 (sp. gr. 1.16) and 

 10-15 cc. distilled water; (2) heat in autoclave for 15 minutes 

 at 15 pounds, cool and neutralize to phenolphthalein by addition 

 of NaOH; (3) dilute and estimate as - 1 -?ose. 



