166 ANIMAL PHYSIOLOGY. 



flow is augmented by flesh, diet, but not by a diet consisting 

 exclusively of fat. 



124. Within the substance of the liver another product 

 besides bile is found, namely, glycogen (Bernard). This, which 

 is likewise called the amyloid substance of the liver, is a material 

 similar to starch or dextrin, of the same chemical composition, 

 and easily converted into sugar. It is obtained as a white 

 powder by precipitation in alcohol from a filtered extract of 

 boiled and pounded liver. It is stored in the hepatic tissue, 

 probably within the cells, and after death is speedily converted 

 in considerable quantities into sugar, which is found in the 

 blood-vessels of the organ. For, if a liver newly excised 

 from an animal have the vessels washed out with water in- 

 jected through the portal vein till it is quite free from sugar, 

 in a few hours afterwards, if they are again washed out, 

 abundance of sugar will be obtained. What becomes of the 

 glycogen during life, however, is a point on which some 

 difference of opinion exists; but it may be mentioned that 

 even those who are most sceptical of its passage during life 

 into the blood, have themselves found sugar in at least minute 

 quantities in blood drawn from the right side of the heart 

 of living animals by means of a pipette introduced by the 

 jugular vein (Pavy and McDonnell): and the student will 

 recollect that it has been already pointed out (p. 109) that 

 the smallness of the quantity of any substance in the blood 

 is no proof that a large amount of it does not pass through 

 the circulation, but only shows that it does not accumulate 

 there. The sugar which enters the circulation from the liver 

 is, in health, destroyed or altered in the lungs. 



Analyses of the livers of animals which had been fed for 

 several days on one particular diet, show that glycogen ac- 

 cumulates most rapidly when the diet consists of starch and 

 sugar, but that it is also formed from purely, nitrogenous 

 food; while, when fat and gelatin alone are consumed, the 

 liver is free from glycogen (McDonnell). % 



125. The blood, in passing through the liver, undergoes a 

 marked amount of change. This is known by analysis of 

 the blood entering by the portal vein, and that which leaves 

 by the hepatic. The blood of the hepatic vein is of very 

 dark colour, and its corpuscles resemble those of the splenic 



