430 HANDBOOK OF PHYSIOLOGY. 



than the meat supplies, in which case he would lose weight but would 

 not lose flesh. 



The proteids of food are described by Voit as having two relations 

 to the proteid metabolism and to outgoing urea; the first part going tc 

 maintain the ordinary and quiet metabolism of the tissues, for which 

 purpose it is actually built up into their molecule, and the second part 

 causing a more rapid formation of urea and rapid proteid metabolism, 

 but never forming a part of the actual protoplasmic molecule. The 

 former proteids are called morphotic or tissue proteids, the latter circu- 

 lating or floating proteids. Normally more proteid is eaten than is 

 needed to supply proteid waste. Pfliiger has pointed out, however, that 

 the tissues must have an excess of proteid to destroy in order to perform 

 their metabolic processes normally. This use of the proteids to form by 

 their oxidation heat and not to produce tissue was looked upon by the 

 older physiologists as a wasteful use of good material, and was called a 

 luxus consumption. 



The condition of nitrogenous equilibrium (i.e., the income and out- 

 put being equal) is one which may be maintained even if the amount of 

 proteid taken as diet far exceeds the necessities of the economy, the urea 

 being excreted in excessive amount, and the wasteful use of proteid food 

 which is so common may not be attended with harmful consequences, 

 so long as the liver is able to do its work in the formation of urea. The 

 body may or may not increase in weight, but if the liver strikes work 

 from any cause, a condition of lithiasis, or of gout, follows. 



It has not actually been proved, but it is not unlikely, that even in 

 the condition of lithiasis, the nitrogen of the ingesta may not greatly 

 exceed that of the egesta, but that the mode of elimination is different. 

 It is only in cases of growth or putting on of flesh, as in growing chil- 

 dren, that nitrogen is retained in the body, except to a very small amount, 

 in health. 



According to calculations which have been made, it appears that 

 the body puts on thirty grammes of flesh for every gramme of nitrogen 

 so retained. 



As regards the retention of carbon in the body, it is calculated that 

 one gramme and a half of weight is put on for each gramme by which 

 the ingesta of carbon is greater than the egesta. 



The Effect of an Albuminoid Diet. The albuminoid which is eaten 

 in greatest quantity is gelatin. Though gelatin closely resembles the 

 proteid molecule chemically, it cannot replace the proteid of the food. 

 In other words, nitrogenous equilibrium cannot be maintained on a diet 

 consisting of gelatin, carbohydrates, and fats. Proteid food is abso- 

 lutely essential to the reconstruction of the proteid molecule. Gelatin 

 is one of the proteid substances which does not have any food value, 



