9o2 METABOLISM. 
found in the liver cells during absorption. We must, it is true, assume 
that when fat is present in the food, the fat which occurs in the liver 
cells during absorption is derived from it : for the absorbed fat, after 
passing through the columnar epithelium cells, in which there is little 
doubt that it undergoes metabolic changes, gets into the thoracic duct, 
and so into the blood, in which it is carried to the liver and elsewhere. 
Nevertheless, in the absence of fat from the food, any fat which is 
found within the liver cells may be supposed to be obtained from 
proteid after the splitting off of the elements of the urea molecule ; 
but we must suppose a considerable breaking - down and a re- 
synthesis to occur. In both carbohydrate and fat formation we must 
recognise the possibility of the preliminary splitting of the proteid 
molecule occurring elsewhere than in the liver, although there is no 
reason to suppose that the protoplasm of the hepatic cell does not 
possess, in common with protoplasm in general, the power to produce 
this change. The possibility of fat being formed from proteid is shown 
by the fact that in dogs subjected to a twelve-day period of inanition, 
and to which phosphorus is then administered, the liver contains from 
two to four times as much fat as in the normal animal — the amount 
of fat in the muscles being also greatly in excess of the normal amount. 1 
This question of the formation of carbohydrate and of fat from proteid, 
both within the liver cells and elsewhere, will be considered later on. 
The circumstances that in mammals urea, and in birds uric acid, 
occur in a larger proportion in the liver than in any other organ in the 
body, that there is an increase of urea in blood which has been passed 
through the liver, provided such blood is derived from an animal during 
absorption of proteid food, and that if blood containing certain ammonia 
compounds is passed through the liver it receives a very appreciable 
addition of urea, 2 all point to the fact, which is now unquestioned, that 
urea and uric acid are produced, if not exclusively, at all events mainly, 
in this organ. 
But the urea which is found in the liver, and which is passed by the 
hepatic capillaries into the hepatic blood, although ultimately derived 
from the proteids of the food, is in all probability not to any appreciable 
extent immediately so derived. If this were to be the case, we shoidd 
have, as with the formation of leucine and tyrosine in the intestine, so 
far as the tissues generally are concerned, a waste of nutritive material — 
a condition which is unlikely to obtain to any extent in the animal 
economy. It may therefore be taken for granted that the great part of 
the proteid which is absorbed from the intestine passes on through the 
hepatic veins into the general circulation, without being stored or at 
once modified in the liver ; and since, after the absorption of any large 
amount of proteid from the alimentary canal, the relative and absolute 
amount of proteid in the blood and lymph is not materially altered, we 
may assume that the excess proteid is stored somewhere else. 
The place of such storage is probably not far to seek. The fact that 
an increase of assimilated proteid in the blood rapidly increases the 
metabolism of muscles, points at once to such proteid passing into the 
1 Storch, Diss., Kjobenliavn, 1865 ; Deutsches Arch. f. klin. Med., Leipzig, 1867, Bd. ii. 
S. 264 ; Bauer, Ztschr. f. Biol., Miinchen, 1871, Bd. vii. S. 63 ; 1878, Bd. xiv. S. 527 ; 
Caseueuve, Rev. mens, demid. ctchir., Paris, 1880, tome iv. pp. 265, 444 ; Stolnikow. Arch, 
f. BhysioL, Leipzig, 1887, Suppl., S. 1. 
2 v. Schroder, Arch. f. cxper. Bath. u. Bharmakol., Leipzig, 1882, Bd. xv. S. 364 ; 
ibid., 1885, Bd. xix. S. 273 ; Salomon, Virchow's Archiv, 1884, Bd. xcvii. S. 149. 
