372 STUDIES IN ADVANCED PHYSIOLOGY. 



world : Persons are able to maintain a financial equilibrium 

 with a small income, but there is no difficulty at all in soon 

 adjusting one's self to an added income and so establishing 

 an equilibrium on a higher level. 



But this does not always mean that when a body is not 

 losing in weight it is holding its own in the fullest sense. 

 It is doing so at a low nutritive level, but it is still starva- 

 tion, and the general beneficial effects that are recognizable 

 in a community of well-fed people clearly argues the physi- 

 ological necessity of establishing in a healthy body at least a 

 medium, still better, a high nutritive equilibrium. 



These metabolic changes and the final products have 

 been fairly well determined only in the case of muscular 

 tissue. What the final chemical changes are in glands 

 ganglia and in nerve fibers, is still a wholly closed book. 

 However, from a merely physical and chemical standpoint 

 the energies liberated by the muscles are by far the bulk of 

 the body's whole expenditure. 



By way of summary, then, we have to ascribe to the 

 main classes of foods these nutritive values: 



First. Proteids. (a) All new tissue, that is, all living tis- 

 sue which has not replaced the old, but is an actual addition, 

 can only be built up from the proteids of the blood and lymph. 

 Hence the somewhat larger proportion of proteids needed 

 in the diet of animals which are in the growing period. 

 (b) Excesses of proteids are broken up in the liver into a 

 non-nitrogenous portion which may appear there as sugar 

 or as fat, and a nitrogenous portion appearing as urea. The 

 sugar or fat so produced from these proteids will then figure 

 just as the other fats and sugars. 



Second. The Albuminoids. These do not figure in an 

 important way, and it is highly improbable that the nitro- 

 gen which they contain can in any material way be utilized 

 like the nitrogen of proteids. Probably the albuminoids 

 figure in the same role as the sugars and the fats. 



Third. TJic Sugars and the Fats. These are the non- 



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nitrogenous foods, but in the tissues these non-nitrogenous 



