422 MANUAL OF PHYSIOLOGY. 



other undergoes changes, probably in the same organ, which re- 

 sult in its being converted into fat. 



It would further seem probable, from the manner in which the 

 urea excretion changes during starvation, that, as before men- 

 tioned, the absorbed albumin exists in the economy in two forms: 

 one in which it has been actually assimilated by the nitrogenous 

 tissues and forms part of them, and hence is called organ-albumin ; 

 the other, which is merely in solution in the fluids of the body, 

 being in stock, but not yet absolutely assimilated, and hence 

 called circulating albumin. The latter passes away during the 

 first few days of starvation, being probably broken up to form urea, 

 and a material which serves the turn of non-nitrogenous food. 

 The organ-albumin only appears to be used for the formation of 

 urea after the circulating albumin has completely disappeared. 



From the foregoing it will be gathered that we cannot say what 

 are the exact destinies of the various food-stuffs in the body. 

 Proteids are not exclusively utilized in the reintegration of pro- 

 teid tissues, as an excess gives rise to a deposit of fat. Carbohy- 

 drates are not turned into glycogeu in the tissues simply to replace 

 the carbohydrates used, but as will be shown when speaking of 

 muscle metabolism, they are intimately related to the chemical 

 changes which take place during the activity of that tissue. If 

 fats are chiefly devoted to the restitution of the fat of the body, 

 they certainly are not the only kind of food from which fat can 

 be made. 



We may say, then, that all food-stuffs are destined to feed the 

 living protoplasm, whether it be in the form of gland cells, the 

 cells of the connective tissues, or muscle-plasma, so that all the 

 food-stuffs that are really assimilated, contribute to the mainte- 

 nance of protoplasm and subserve to its various functions. Be- 

 sides nourishing itself and keeping itself up to a certain standard 

 composition, protoplasm, or rather the various protoplasraata, 

 can make the various chemical materials we find in the body. 

 Some produce fat, some animal starch (glycogen), and others 

 manufacture the various substances we find in the secretions ; while 

 yet another group is devoted to setting free and utilizing the 

 energy of the various chemical associations. 



