METABOLISM, NUTRITION AND DIETETICS 541 



The Oxygen Deficit. The carbo-hydrates contain in themselves 

 enough oxygen to form water with all their hydrogen ; they account 

 for a part of the water-formation in the body, but for none of the 

 oxygen deficit. 



The fats are very different ; their hydrogen can be nothing like 

 completely oxidized by their oxygen. A gramme of hydrogen is 

 contained in 8*5 grammes of dry fat, and needs 8 grammes of oxygen 

 for its complete combustion. Only i gramme of oxygen is yielded 

 by the fat itself ; so that if a man uses i oo grammes of fat in twenty- 

 four hours, rather more than 80 grammes of the oxygen taken in 

 must go to oxidize the hydrogen of the fat. 



The proteins also contribute to the deficit. In 100 grammes of 

 dry proteins there are 15 grammes of nitrogen, 7 grammes of 

 hydrogen, and 21 grammes of oxygen. The carbon does not concern 

 us at present. The 33 grammes of urea, corresponding to 100 

 grammes of protein, contains 15 grammes of nitrogen, a little more 

 than 2 grammes of hydrogen, and a little less than 9 grammes of 

 oxygen. There remain 5 grammes of hydrogen and 12 grammes of 

 oxygen. But 5 grammes of hydrogen needs for complete combustion 

 40 grammes of oxygen ; therefore 28 grammes of the oxygen taken 

 in must go to oxidize the hydrogen of 100 grammes of protein. 

 Taking 140 grammes of protein as the amount in a liberal diet for 

 a man, we get 39 grammes as the required quantity of oxygen. This, 

 added to the 80 grammes needed for the hydrogen of the fat, makes a 

 total of, say, 120 grammes, equivalent to about 85 litres of oxygen. 

 A small amount of oxygen also goes to oxidize the sulphur of proteins. 



With a diet containing less fat and protein and more carbo- 

 hydrate, the oxygen deficit would of course be less. 



The Production of Water in the Body. One gramme of hydrogen 

 corresponds to 9 grammes of water. In 140 grammes of proteins 

 and 100 grammes of fat there are, in round numbers, 22 grammes 

 of hydrogen ; in 350 grammes of starch, 21*5 grammes. With this 

 diet, 43 '5 grammes of hydrogen is oxidized to water within the body 

 in twenty-four hours, corresponding to a water production of 391 

 grammes, or 1 5 to 20 per cent, of the whole excretion of water. It 

 has been observed that during starvation the tissues sometimes 

 become richer in water, even when none is drunk. The only explana- 

 tion is, that the elimination of water does not keep pace with the 

 rate at which it is produced from the hydrogen of the broken-down 

 tissue-substances, or set free from the solids with which it is 

 (physically ?) united. 



Inorganic Salts. The inorganic salts of the excreta, like 

 the water, are for the most part derived from the salts of the 

 food, which do not in general undergo decomposition in the 

 body. A portion of the chlorides, however, is broken up to yield 

 the hydrochloric acid of the gastric juice. Within the body some 

 of the salts are more or less intimately united to the proteins of 

 the tissues and juices, some simply dissolved in the latter. 

 The chlorides, phosphates and carbonates are the most im- 

 portant ; the potassium salts belong especially to the organized 

 tissue elements, the sodium salts to the liquids of the body ; 

 calcium phosphate and carbonate predominate in the bones. The 

 amount and composition of the ash of each organ only change 



