58 G. F. Barker—Physiological Chemistry. 
of all reducing substances. Ritter believes that the use of pure 
solutions of cupric sulphate and of potassic hydrate, mixed 
only when used, prevents many errors which arise from the use 
of tests prepared beforehand with some organic substance. 
That the failure of the reaction in the above experiments was 
not due to the presence of a substance which either prevented 
the oxydation of the sugar or masked in some way the reaction, 
is shown: Ist, by the fact that no other test detected sugar ; 
and 2nd, that on digesting the liver-extract with saliva or boil- 
ing it with a dilute acid, it afforded the reaction distinctly. 
Moreover, a solution of the same liver, less rapidly prepared, 
reduced readily the copper-tests. A series of experiments were 
then made by taking a number of capsules containing boilin 
water, and in the first, converting a piece of liver into extract 
at once, as above; a second piece of liver was then taken, the an- 
imal having died meanwhile, and treated in the second capsule ; 
in the third, a third piece was treated, taken still later ; and so 
on. All the solutions thus prepared, excepting only the first, 
reduced the copper-tests ; the reaction always being stronger, 
the longer after death the piece was taken ; thus proving that 
the absence of sugar in the first specimen is due to the fact 
that the time was too short for the post-mortem changes to take 
place. Bernard admits only an increase of the sugar after 
death ; these experiments show that it is rather a production 
of this substance. If the pieces put into boiling water are 
moderately large, then the heat penetrates them slowly and 
sugar is found in the extract. Ritter finds therefore that it is 
better to divide them finely, since there is less change during this 
process than during the time required for the heat to penetrate 
a large mass. These experiments, repeated a great number 0 
gles interfere with the liver-circulation and sugar is produced 
in that organ, even before death. The dogs were killed by a 
blow on the head, and liver was instantly examined ; no sugar 
was found in it, though glycogen was abundant. Ritter finds 
moreover, that Bernard’s method of removing hepatic venous 
blood is faulty, since the time occupied in in Pere and ligating 
these veins, suffices to cause the production of sugar in the liver. 
The easiest mode of procuring pure hepatic blood is to cathe- 
terize the right ventricle, since hepatic blood constitutes a large 
