356 EQUILIBRIUM OF THE METABOLISM. 



are given off by the urine ; the less soluble salts, especially those of potash, and 

 the insoluble salts, in the faeces ; while others are given off in the sweat. Of the 

 sulphur of albumin, about one-half is excreted in the sulphur compounds in the 

 urine, and the other half in the faeces (taurin) and in^the epidermal tissues. 



Every organism has a minimum and a maximum limit of metabolism, according 

 to the amount of work done by the body, and its weight. If less food be given 

 than is necessary to maintain the former, the body loses weight ; while, if more be 

 given after the maximum limit is reached, the food so given is not absorbed, but 

 remains as a floating balance, and is given off with the faeces. When food is 

 liberally supplied and the weight increases, of course the minimum limit rises ; 

 hence, during the process of "feeding" or "fattening," the amount of food necessary 

 is very much greater than in poorly fed animals, for the same increase of the body- 

 weight. By continuing the process, a condition is at last reached, in which the 

 digestive organs are just sufficient to maintain the existing condition, but cannot 

 act so as to admit of new additions being made to the body-weight {v. Bischqf, v. 

 Voitj v. Pettenkofer). 



By the term " luxus consumption " is meant the direct combustion or oxidation 

 of the superfluous food-stuffs absorbed into the blood. This, however, does not 

 exist ; on the contrary, the material in the juices is always being used for building 

 up the tissues. The albumin found in the fluids, which everywhere permeate the 

 tissues, has been called " circulating albumin," and according to v. Voit it 

 undergoes decomposition sooner than the organised or " organic albumin " which 

 forms an integral part of the tissue. According to v. Voit, in 24 hours 1 per cent, 

 of the organic and 70 per cent, of the circulating albumin is used up. 



[Liebig taught that the nitrogenous metabolism of the body depended on a corresponding 

 decomposition of the proteids of the organs, so that the proteids in the food supplied the place 

 of tin- proteids of the organs thus used up. He called the proteids " plastic foods " or "tissue 

 formers," while he regarded the fats and carbohydrates as "respiratory foods," as he supposed 

 that they alone were concerned in the evolution of heat. As a matter of fact, experiment 

 proved that the N metabolism is to a large extent independent of the proteids of the food. The 

 liixus-consumption theory was invented to explain this. It simply means, that proteids taken 

 with the food not only replace the amount of proteids which have been decomposed during the 

 activity of organs and tissues, but that any excess is immediately consumed without being con- 

 verted into tissue, and thus this surplus amount giving rise to heat, by being oxidised, to a certain 

 extent replaces the fats and carbohydrates. But Voit showed that nitrogenous metabolism is 

 not influenced by the activity of the organism, and he proved that in ordinary conditions, only 

 a small amount of the organic albumin, i.e., that composing tissues and organs, undergoes 

 decomposition, while, owing to the action of the cellular elements of the tissue, a large amount 

 of the circulating albumin is split up, so that under ordinary conditions, the organic albumin is 

 comparatively stable. This he demonstrated from a comparison of the urea excreted, for the 

 urea may be taken as an index of the N metabolism in well-fed, fasting, and starving animals. 

 But in certain pathological conditions the organic albumin may undergo rapid change, having 

 become less stable, as in fevers, and poisoning with phosphorus.] 



Quality and Quantity of the Diet. As far as his organisation is concerned, man 

 belongs to the omnivorous animals, i.e., those that can live upon a mixed diet. For 

 an adequate diet man requires for his existence and to maintain health a mixture 

 of the following four chief groups of food-stuffs along with the necessary relishes ; 

 none of them must be absent from the food for any length of time. They are : 



1. Water for an adult in his food and drink, 2700 to 2800 grms. [70 to 90 

 oz.] daily ( 229 and 247, 1). 



[Thirst. The needs of the economy for water are expressed by the sensation of thirst. The 

 sensation of heat and dryness may be confined to the tongue, mouth and fauces, and indeed 

 may be excited by inhaling dry air. This local thirst may be allayed by swallowing water or 

 by eating substances which excite the secretion of saliva. More frequently, however, the 

 sensation is the expression of a general condition indicating the diminution of water in the 

 tissues ; or it may be due to excess of saline matters in the blood. In some diseases this sensation 

 is very intense, e.g., diabetes. If water be injected into the blood-vessels, or stomach, both the 

 general and local thirst are abolished, even although no water enters the mouth. ] 



