308 PHYSIOLOGICAL CHEMISTRY 



ing 1 mg. of sugar per 10 c.c (5 c.c. of the stock solution diluted 

 to 500 c.c.) ; (3) a solution containing 2 mg. of sugar per 10 

 c.c. (5 c.c. of the stock solution diluted to 250 c.c.). The invert 

 sugar solution has the advantage that it can be easily prepared 

 from cane sugar, which is pure. The keeping quality of such 

 solutions should be less good than those made from glucose, but 

 we have encountered no trouble on that score. When good 

 quality glucose is available, it is, of course, the one to use. The 

 diluted solutions should be preserved with a little added toluene 

 or xylene; it is probably better not to depend on such diluted 

 solutions to keep for more than a month, but the stock solution 

 should keep indefinitely. 



Determination. The blood sugar determination is now made 

 as follows : 



Transfer 2 c.c. of the tungstic acid blood filtrate to a blood 

 sugar test tube, and to two other similar test tubes (graduated 

 at 25 c.c.) add 2 c.c. of standard sugar solution containing re- 

 spectively 0.2 and 0.4. mg. of dextrose. To each tube add 2 

 c.c. of the alkaline copper solution. The surface of the mix- 

 tures must now have reached the constricted part of the tube. 

 If the bulb of the tube is too large for the volume (4 c.c.) a 

 little, but not more than 0.5 c.c. of a diluted (1:1) alkaline cop- 

 per solution may be added. If this does not suffice to bring 

 the contents to the narrow part, the tube should be discarded. 

 Test tubes having so small a capacity that 4 c.c. fills them 

 above the neck should also be discarded. Transfer the tubes to 

 a boiling water bath and heat for 6 minutes. Then transfer them 

 to a cold water bath and let cool, without shaking, for 2 or 3 min- 

 utes. Add to each test tube 2 c.c. of the molybdate phosphate 

 solution. The cuprous oxide dissolves rather slowly if the 

 amount is large but the whole, up to the amount given by 0.8 

 mg. of dextrose, dissolves usually within 2 minutes. When the 

 cuprous oxide is dissolved dilute the resulting blue solutions 

 to the 25 c.c. mark, insert a rubber stopper, and mix. It is 

 essential that adequate attention be given to this mixing be- 



