METABOLISM. 69 



have first to note those various minor transformations that 

 are auxiliary to the general transformation by which force is 

 obtained from food. For many of the vital activities merely 

 subserve the elaboration of materials for activity at large, 

 and the getting rid of waste products. From blood passing 

 through the salivary glands is prepared in large quantity a 

 secretion containing among other matters a nitrogenous fer- 

 ment, ptyaline, which, mixed with food during mastication, 

 furthers the change of its starch into sugar. Then in the 

 stomach come the more or less varying secretions known in 

 combination as gastric juice. Besides certain salts and 

 hydrochloric acid, this contains another nitrogenous ferment, 

 pepsin, which is instrumental in dissolving the proteids 

 swallowed. To these two metabolic products aiding solution 

 of the various ingested solids, is presently added that pro- 

 duct of metabolism in the pancreas which, added to the 

 chyme, effects certain other molecular changes — notably that 

 of such amylaceous matters as are yet unaltered, into sac- 

 charine matters to be presently absorbed. And let us note 

 the significant fact that the preparation of food-materials in 

 the alimentary canal, again shows us that unstable nitrogenous 

 compounds are the agents which, while themselves changing, 

 set up changes in the carbo-hydrates and proteids around: 

 the nitrogen plays the same part here as elsewhere. It does 

 the like in yet another viscus. Blood which passes through 

 the spleen on its way to the liver, is exposed to the action 

 of " a special proteid of the nature of alkali-albumin, hold- 

 ing iron in some way peculiarly associated with it." Lastly 

 we come to that all-important organ the liver, at once a 

 factory and a storehouse. Here several metabolisms are 

 simultaneously carried on. There is that which until recent 

 years was supposed to be the sole hepatic process — the 

 formation of bile. In some liver-cells are masses of oil- 

 globules, which seem to imply a carbo-hydrate metamor- 

 phosis. And then, of leading importance, comes the exten- 

 sive production of that animal-starch known as glycogen — a 



