92 Dk. Mitchell on the Occurrence of Siujar in the Animal Economy. 



of applying it when examining animal fluids, of which I shall enumerate 

 two. 1st, Precipitate the protein compounds by anhydrous alcohol, and 

 add dry carbonate of potash to the filtered spirituous solution. On the 

 addition of a little sulphate of copper and the application of heat, we 

 observe, if sugar be present, a yellow or yellowish brown tint developed, 

 produced by the reduction of the copper to a state of suboxide. This is 

 the method which was employed by Simon in his elaborate researches in 

 animal chemistry, and Trommer states that its delicacy is sufficient to 

 detect one grain of sugar in 10,000 of blood. I can affirm myself that 

 sugar may be detected in a solution of twice that strength, which is still 

 a state of extreme dilution. 



A second method of procedure is the following : — When the blood is 

 extracted from the heart or vessels, it is left to coagulate ; then taking a 

 portion of the serum which separates in a test tube, add about a sixth of 

 its volume of the double tartrate of copper and potash ; then boiling the 

 mixture, a reduction of the salt of copper will be effected proportional to 

 the quantity of sugar contained in the serum. This mode of operating 

 is very simple, very rapid, and very delicate ; and in making comparative 

 experiments it is all that is required. It is that which has been adopted 

 by Bernard, Barreswill, and Mialhe in their various researches on the 

 digestion of feculents. 



M. Ferrand has proposed another method, which I find very accurate, 

 but not always readily applied. The blood of the animal is received into 

 boiling water, which separates, by coagulation, the albumen and fibrin, 

 and retains the substances soluble. The liquid is filtered, rendered 

 neutral by some drops of acid, and evaporated gently; the residue treated 

 with alcohol, &c. aa in the former cases. 



Although this test, employed in either of these three ways, is most 

 valuable in comparative experiments, yet for additional security occasional 

 recourse must be had to others. Among these, the fermentation test decid- 

 edly stands first. A small quantity of barm is added and the gas collected 

 in a suitable apparatus. If the quantity of sugar be too small to give the 

 products of fermentation sufficiently distinct, various plans are employed, 

 and one of the best is that proposed by Dr. M'G-regor of Glasgow. The 

 serum is coagulated by heat, and carefully dried on a steam bath. The 

 solid clot is divided as minutely as possible and boiled in water ; this is 

 then filtered and evaporated to a cei'tain extent. To the concentrated 

 fluid the yeast is then added. When the fermentation test is applied in 

 its widest bearings, I conceive it to be absolutely conclusive of the pre- 

 sence of sugar. If the gas given ofl" be proved, by suitable tests, to be 

 carbonic acid, and if the liquid left be shown, by distillation, to contain 

 alcohol, I think all will assert that sugar must have existed in the fluid, 

 And such proof have I of the occurrence of sugar in the liver. The 

 specimen of spirit which I have in my hand, sufficiently concentrated to 

 be inflammable, is the result of the distillation of a calf's liver. It was 

 purchased in the market immediately after the animal was killed, and 



