472 THE HUMAN BODY. 



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, except for its dis- 

 charge into the blood instead of a gland duct, would then be 

 comparable to the materials stored in the cells of the salivary 

 and some other glands (Chap. XIX); and the transforma- 

 tion 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 simultaneous 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, 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 require some time, before it can be taken 

 into the blood and carried off to other parts. 



When adipose tissue is developing it is seen that undif- 

 ferentiated cells in the connective tissues (especially areolar) 

 show minute oil-drops in their protoplasm; these increase 

 in size and ultimately fuse together and form one larger 

 oil-droplet, while most of the original protoplasm disappears. 



The oily matter would thus seem due to a chemical meta- 

 morphosis of the cell protoplasm, during which it gives rise 

 to a non-azotized fatty residue which remains behind, and *a 

 highly nitrogenous part which is carried off. In many parts 

 of the Body protoplasmic masses are subject to a similar but 

 less complete metamorphosis; fatty degeneration of the heart, 

 for example, is a more or less extensive replacement of the 

 proper substance of its muscular fibres by fat-droplets; and 

 the cream of milk and the oily matter of the sebaceous secre 



