SUGAES. 55 



It is a curious fact that sugar added to healthy urine, even 

 in large quantity, will not respond to Trommer's test, on 

 account of organic matters, which interfere with the reduc- 

 tion of the copper. The cause of this interference we do not 

 understand ; but in diabetes, the organic substances, whatever 

 they may be, are not present, or at least do not interfere with 

 the application of tests for sugar. 



Another precaution to be adopted is to add a small quan- 

 tity, two or three drops only, of the solution of sulphate of 

 copper, especially if we suspect the sugar to be present in 

 small quantity ; for if too much be added, a portion only of 

 the oxide of copper will be reduced, and that which remains, 

 by its blue color, may obscure the reaction. 



BarreswiWs Test. For those engaged in physiological 

 investigations, when it is desired to roughly estimate the 

 quantity of sugar in any clear extract, and when the test is 

 to be employed very frequently, Barreswill's solution is con- 

 venient. This is simply a solution of tartrate of copper and 

 caustic potash. The reaction with this fluid is precisely the 

 same as in Trommer's test. It has seemed to me, if there be 

 any difference, that the reduction takes place more promptly 

 with the sulphate of copper, but that the tartrate will detect 

 a smaller quantity of sugar. The advantage of Barreswill's 

 test is, that but a single fluid is to be added to the suspected 

 solution. The only disadvantage is, that the solution is liable 

 to alteration if kept more than a few days or weeks. After 

 standing for a certain time, a yellowish sediment is deposited, 

 and the fluid will no longer reduce in the presence of sugar. 

 Its properties may be renewed by adding a little potash and 

 filtering ; but in delicate observations, it is always better to 

 use a solution which has not undergone alteration. 



In employing this test, we add to the suspected fluid 

 enough of the solution to give the whole a distinctly blue 

 color, and boil ; if sugar be present, we have a reduction of 

 the yellowish sub-oxide of copper as in Trommer's test. 



