FATS. 443 



glycogen is turned into glucose in a given time, and carried off 

 by the hepatic veins. If the splanchnic nerves be cut the 

 whole arteries of the abdominal viscera dilate and no diabetes, 

 follows, because so many vessels being dilated a great part 

 of the blood of the Body accumulates in them, and there is 

 no noticeably increased flow through the liver. Others, 

 however, maintain that the "piqure " diabetes (as that due 

 to pricking the medulla is called) is due to irritation of 

 trophic nerve-fibres originating there, and governing the 

 rate at which the liver-cells produce glycogen or convert it 

 into glucose. This latter view, though perhaps the less- 

 commonly accepted, is probably the more correct. The 

 hepatic cells do not merely hold back glucose carried 

 through the liver so that it is there to be washed out by a 

 greater blood-flow, but they feed on sugar and proteids 

 and make glycogen; and this is later converted into glucose 

 and carried off. Glycogen is thus comparable to the zymo- 

 gen of the pancreas and other glands (Chap. XVIII.); and 

 the transformation of such bodies into the specific element 

 of a secretion we have already seen to be directly under the 

 control of the nervous system, and almost entirely or quite 

 independent of the blood-flow. 



The History of Fats. While glycogen forms a reserve 

 store of material which is subject to rapid alterations, deter- 

 mined by meal-times, the fats are much more stable; their 

 periods of fluctuation are regulated by days, weeks, or 

 months of good or bad nutrition, and during starvation they 

 are not so readily, or at least so rapidly, called upon as the 

 hepatic glycogen. If we carry on the simile by which we 

 compared the reserve in each cell to pocket-money (p. 31), 

 the glycogen would answer somewhat to a balance on the 

 right side with a man's banker ; while the fat would 

 represent assets or securities not so rapidly realizable; as 

 capital in business, or the cargoes afloat in the argosies of 

 Antonio, the "Merchant of Venice." Fat, in fact, is 

 slowly laid down in fat-cells and surrounded in these by a 

 cell-wall, and, being itself insoluble in blood plasma or 

 lymph, it must undergo chemical changes, which no doubt 



