9 24 METABOLISM. 
himself, that when the blood from the hepatic vein is collected under 
conditions of anaesthesia, the difference between the percentage amount of 
sugar in the hepatic blood and that in ordinary arterial blood becomes 
greatly diminished, if it does not altogether disappear. 1 
Bernard's views have been combated strenuously by Pavy, 2 whose 
method of experimentation is not open to the same objection as that 
of Seegen and others who have found a constant excess of sugar in 
the hepatic blood. Pavy takes blood from the animal immediately 
after it has been killed by a blow upon the head, and before there 
has been time for any change to have occurred in the liver, and he 
finds that blood which is collected under these circumstances from 
the inferior vena cava (including, therefore, the blood which has passed 
out from the liver) never shows any appreciable excess of reducing 
substances over blood obtained from other parts of the body. Eesults 
similar to those of Pavy have also been obtained, although under 
somewhat different conditions, by other observers. 
We are therefore landed in this difficulty, as the result of the 
imperfection of our present methods, that we cannot be sure whether 
the blood of the hepatic vein does or does not, normally, contain an 
excess of sugar. If it does, we are bound to assume that sugar is 
being continually passed off from the liver into the general blood of the 
body, and since this sugar does not pass off by the urine, it can only be 
available for the nutrition of the tissues, and the production of energy 
by oxidation. If sugar does not pass from the liver into the blood, we 
should require to find some form in which the glycogen, which is 
undoubtedly stored up in the liver, is got rid of, and also to find some 
meaning for its presence there and in the muscles. 
It has been suggested by Pavy 3 that such stored glycogen may 
become converted into fat. There is no doubt that carbohydrate 
food does become converted in the body into fat, and there are 
many instances of the formation of fat from carbohydrate material in 
plants ; it is therefore not altogether wanting in probability, that the 
glycogen which is stored up in the liver cells and muscles may also 
become converted into fat. Such fat may be assumed to be gradually 
removed by the blood and carried to the different organs, and in them 
ultimately oxidised to carbonic acid and water. 
Another supposition, which we have already considered, is that it 
becomes directly oxidised, and produces heat. As most of the 
oxidation of the body occurs in the muscles, and as the muscles retain 
their glycogen in starvation longer than the liver, although the latter 
organ contains normally a much larger proportion, it seems very 
probable that the glycogen passes from the liver to the muscles. This 
cannot be as glycogen, for glycogen is not present in blood plasma, and 
J Ccntralbl.f. Physiol, Leipzig u. Wien, 1S96-97, Bd. x. S. 497, 822. 
- ••The Physiology of the Carbohydrates," London, 1894. Here other papers by the 
.same author are referred to. 
s Ibid., pp.245 to 252. In connection with the question of sugar production by the 
liver, it may be mentioned that removal of this organ or cutting off its blood supply in 
rabbits (Bock and Hoffmann, " Exper. Studien ii. Diabetes," Berlin, 1S74), dogs (Seegen. 
"Die. Zuckerbildung," and Tanyl and v. Harley, Arch. f. d. ges. Physiol., Bonn, 1895, 
Bd. lxi. S. 551), geese (Minkowski, Arch. f. exper. Path. u. Phcwrmakol., Leipzig, 1882, 
Bd. xx. S. 41), is followed by either disappearance or marked diminution of the sugar of the 
blood. 
