352 THE ADRENAL, GENERAL MOTOR, AND VAGAL SYSTEMS. 



was commensurate with the amount of blood that the arterioles 

 supplied to the contractile tubular elements. There seems to 

 be considerable analogy between this process and that which 

 prevails in the hepatic lobule. Howell alludes to this in the 

 following words, which well recall the fact that we referred to 

 glycogen as the main constituent of myosinogen: "The history 

 of glycogen is not complete without some reference to its oc- 

 currence in the muscles. Glycogen is, in fact, found in various 

 places in the body, and is widely distributed throughout the 

 animal kingdom. It occurs, for example, in leucocytes, in the 

 placenta, in the rapidly-growing tissues of the embryo, and in 

 considerable abundance in the oyster and other mollusks. But 

 in our bodies and in those of the mammals generally the most 

 significant occurrence of glycogen, outside the liver, is in the 

 voluntary muscles, of which glycogen forms a normal con- 

 stituent." 



The similarity between muscular and hepatic sources of 

 energy is further emphasized when, in the following paragraph, 

 Howell says: "In accordance with the view given above of the 

 general value of glycogen namely: that it is a temporary 

 reserve-supply of carbohydrate material that may be rapidly 

 converted into sugar and oxidized, 22 with the liberation of energy 

 it is found that the supply of glycogen is greatly affected by 

 conditions calling for increased metabolism in the body. Mus- 

 cular exercise will quickly exhaust the supply of muscle and 

 liver glycogen provided it is not renewed by new food. In a 

 starving animal glycogen will finally disappear, except perhaps 

 in traces; but this disappearance will occur much sooner if 

 the animal is made to use its muscles at the same time. It 

 has been shown also by Morat and Dufourt that, if a muscle 

 has been made to contract vigorously, it will take up much 

 more sugar from an artificial supply of blood sent through it 

 than a similar muscle which has been resting; on the other 

 hand, it has been found that, if the nerve of one leg is cut so 

 as to paralyze the muscles of that side of the body, the amount 

 of glycogen will increase rapidly in these muscles as compared 



22 The italics are our own. 



