186 Chittenden and Lambert—Post-mortem Formation 
presence of peptone may, unless certain precautions are taken, inter- 
fere slightly with exact determinations. With the Allihn method, 
variations of 2-5 milligrams in the amount of reduced copper are 
liable to occur if care is not taken in regulating the length of time 
the alkaline copper solution is heated after addition of the sugar 
solution. Under ordinary circumstances results most nearly in ac- 
cord with theory are obtained by adding the sugar solution, as recom- 
mended by Allihn, to the previously heated Fehling’s solution and 
then heating further until bubbles just begin to break upon the 
surface of the liquid. If heated longer, even only half a minute, a 
slight increase in the amount of reduced copper will generally be 
observed. Now whenever peptone is present to any extent in the 
sugar solution, we have found by experience that complete reduc- 
tion does not take place quite so rapidly ; the loss is not great, some- 
times but a milligram or so, still the difference is appreciable. This, 
however, can be avoided by simply allowing the standard copper 
solution to boil for about 45 seconds after the addition of the sugar 
solution. Under such conditions, repeated trials have shown us, that 
the presence of peptone does not offer the slightest obstacle to accu- 
rate determinations of dextrose. Whenever, therefore, in the follow- 
ing experiments the solution to be tested contained peptone, the 
above rule has been invariably followed. 
Determination of total carbohydrates.—F or this purpose 200 ¢. ¢. of 
the liver extract were heated in a closed flask at 100° C. with sufficient 
10 per cent. hydrochloric acid to ensure a content of 2 per cent HCl, 
for 17 hours. The solution was then nearly neutralized, care being 
taken that the fluid did not become alkaline, concentrated and 
finally brought to a volume of 200 c. ¢, in an aliquot portion of 
which the total carbohydrates in the form of dextrose were deter- 
mined in the usual manner, Seegen* states that in the determination 
of total carbohydrates, the fluid, after heating with acid, always 
became very dark, which occasionally interfered somewhat with the 
determination of sugar. Delprat,+ however, states that in bis 
experiments the solution, under like conditions, became brownish 
yellow and generally deposited a flocculent brownish black precipi- 
tate of organic matter. Moreover, in some cases, particularly with 
the livers of dogs, cats and calves, the cuprous oxide, in determining 
total carbohydrates, would remain dissolved to a great extent, thus 
interfering with the accuracy of the volumetric determination, some- 
* Pfliiger’s Archiv, vol. xxviii, p. 121. 
+ Jahresbericht fir Thierchemie, 1881, p. 323-324, 
= 
