ABSORPTION. 209 



glucose from the liver. According to the more recent investigations 

 of Bernard,* the arterial blood of both herbivorous and carnivorous 

 animals, either fasting or in digestion, and that of man, living on a 

 mixed diet, always contains glucose in sensibly the same proportion ; 

 namely, from 1.10 to 1.45 per thousand parts. In its passage through 

 the general capillary circulation, the glucose disappears. The precise 

 changes which it undergoes, and the immediate products of its decom- 

 position, are still unknown, but they no doubt serve in some way for 

 the process of general nutrition. Consequently the venous blood re- 

 turning from the peripheral organs contains less glucose than the arte- 

 rial blood with which they are supplied. In two instances Bernard 

 found in the dog its proportion, in the blood of the carotid artery and 

 jugular vein, as follows : 



Pi:oi'OKTix OF (TLUCOSE IN THE BLOOD. 

 From the Per thousand parts. 



Carotid artery 1.1 -t 1.23 



Jugular vein 0.98 0.81 



In the venous blood of the trunk and lower extremities the same 

 diminution occurs ; but at the level of the hepatic veins the quantity 

 of glucose in the blood suddenly augments to more than double, rising 

 sometimes to a maximum of 2.50 or 3.00 parts per thousand. This 

 proportion is again diminished on its being mingled with the blood of 

 the superior vena cava, and in the right ventricle the maximum is 1.81 

 per thousand parts. 



So far, therefore, we must regard the liver as a temporary deposit 

 for the carbohydrates in the form of glycogen. According to this view, 

 the system requires for its nutrition a constant supply of glucose, to 

 be decomposed in the general circulation. The starchy matters of the 

 food, at each period of digestion, are rapidly converted into soluble 

 glucose, and absorbed from the intestine by the portal blood. On 

 reaching the liver they are reduced to the dehydrated or glycogenic 

 condition, under which form they remain as a reserve material until 

 a further supply shall be received from the food. During this interval, 

 the glycogen is slowly reconverted into glucose, and given up, little 

 by little, to the blood of the general circulation, to be decomposed in 

 the system at large. The proportion of glucose in the blood is thus 

 maintained at nearly a constant standard, notwithstanding the varia- 

 tions in its supply from without. 



Accumulation of Glucose in the Blood, and its Discharge by the 

 Urine. Under ordinary conditions the glucose thus formed does not 

 pas beyond the general circulation. But if from any cause its quantity 

 in the blood be raised above a certain proportion, it fails to be com- 

 pletely assimilated, and a part is discharged by the kidneys, producing 



* Coinptes Kendus de 1' Academic des Sciences. Paris, 1876, tome Ixxxii., pp. 369, 

 407. 



O 



