46 PHYSIOLOGY CHAP. 



organism until the normal condition is regained, i.e. equilibrium 

 of the intake and output (Luciani and Lo Monaco). 



Just as abstinence from iron produces oligochromaemia, a 

 decrease in the haemoglobin of the red corpuscles, so abstinence 

 from calcium produces rickets and osteoporosis. When, for instance, 

 heifers are given food containing only a small quantity of lime, 

 such as turnips, the thickness of the bones decreases, so that they 

 can no longer support the weight of the body, and become bent as 

 in rickets. If, on the other hand, cattle are given plenty of clover 

 and hay which contain a large quantity of calcareous salts, the 

 bones develop well and become firm. 1 



XII. Now that we have studied the influence exercised on the 

 exchange of material by the different substances taken in our 

 food, it will be easy to make a comparative examination of their 

 different uses in the organism, which will serve as the basis for a 

 jtliysiological classification of articles of food. 



Liebig's old division of alimentary substances into plastic and 

 respiratory is clearly erroneous, since the whole group of proteins 

 act at the same time both as plastic foods or constructive material 

 for the tissues and the protoplasm of cells in general and as 

 respiratory foods, that is, material for combustion. Liebig's theory 

 had, however, the merit of recognising the proteins as the elements 

 which are most necessary and indispensable in nutrition, without 

 which the development and the recuperation of the tissues are 

 alike impossible. Genuine flesh, as found in nature, that is, chemi- 

 cally combined with organic substances containing phosphorus and 

 salts, contains all the qualities and functional capabilities of the 

 foods essential to life, even when it is almost entirely lacking in 

 fat and glycogen. It not only possesses plastic and respiratory 

 qualities, but is also able to stimulate metabolism. We have 

 indeed seen that in order to make up for the daily deficit of 

 nitrogen, which exists during a long fast, it is not enough to 

 give daily an equal quantity of nitrogen in the form of proteins, 

 but a considerably larger quantity is required; and during the 

 alimentary regimen the consumption of nitrogen increases 

 within certain limits with the quantity of proteins taken. They 

 therefore intensify metabolism, probably by promoting the trophic 

 activity of the nervous system. 



In order to explain the gradual decrease in the consumption 

 of nitrogen during fasting, and the increase during a normal 

 regimen with the quantity of protein taken in, Voit suggested 

 that circulating proteins, i.e. dead proteins absorbed by the 

 digestive tube, are more easily burnt than the tissue proteins 

 which form the essential basis of living protoplasm. 



This interpretation, however, is not only arbitrary, but also in 

 flat contradiction to the fundamental and traditional theory of 

 1 See also question of vitaniines, p. 49. 



