NOURISHMENT FOR A HEALTHY ADULT. 433 



later completely oxidized into carbon dioxid, it may happen that during 

 one part of a period of dieting more oxygen may be taken up than is given 

 off as carbon dioxid. 



Hydrogen leaves the body principally oxidized into water, but it may 

 also leave the body combined with organic excreta. The water is given off 

 with the urine, the feces, through the lungs and by evaporation from the skin. 

 As hydrogen is oxidized into water the amount of water given off is naturally 

 greater than that taken up. The salts are excreted in various ways, the most 

 soluble of them passing out with the urine, a few, particularly potassium-salts, 

 and those that are soluble with difficulty, with the feces, and some, like com- 

 mon salt, in part also with the sweat. The salts contained in the ingesta 

 and excreta are estimated by weight after incineration. 



If the sulphur and the phosphorus are to be estimated separately the 

 amount of each in the ingested food is oxidized by combustion, by addition of 

 sodium hydroxid and potassium nitrate into sulphuric and phosphoric 

 acids respectively. The same method is followed for their estimation in the 

 feces, as well as for sulphur in the epidermal structures. The sulphuric and 

 phosphoric acids so obtained, as well also as the sulphur and the phosphorus 

 excreted in the urine in an already oxidized form, are estimated according to 

 the method described on p. 491. The sulphur is derived principally from 

 the albuminous food; about half of it is excreted with the urine as sulphuric 

 acid, half with the feces (as taurin) and through the epidermal structures. 



For every body, there is, according to its weight and activity, a 

 minimum and a maximum limit of metabolic balance. If less food is 

 supplied than is necessary for the first, loss of body- weight results. If, 

 on the other hand, an excess of food is supplied, any amount exceeding 

 the maximum limit will be passed unabsorbed as superfluous ballast 

 with the feces, provided it cannot be utilized for increase of flesh. The 

 more the body gains in weight on a generous diet, the higher the mini- 

 mum limit rises. With marked increase of flesh, therefore, the necessary 

 supply of food must be relatively much greater than in the case of thin 

 persons, in order to cause a like increase in the tissues of the body. 

 With continued increase in flesh there finally results a condition in which 

 the digestive organs are able to prepare only sufficient material for the 

 maintenance, but not for increase, of weight. 



QUALITY AND QUANTITY OF NOURISHMENT FOR A HEALTHY ADULT. 



The question as to the substances that are needed by man for his 

 satisfactory nourishment, and the amount required, has naturally been 

 answered in a purely empirical way by observation of the manner of 

 nourishment of healthy individuals at different ages and with varying 

 degrees of activity. As, for example, the infant flourishes and grows on 

 a diet of milk, milk must undoubtedly include in its composition nutrient 

 matter qualitatively and quantitatively appropriate. 



In accordance with his entire organization man beldngs to the 

 omnivora, that is, to the class of beings that is adapted to a mixed diet. 

 He possesses the canine tooth of the carnivora, but his intestine is 

 shorter than that of the herbivora. 



For his continued existence man requires the following four principal 

 nutritive substances, none of which can be spared from the diet for any 

 length of time : 



i. Water; for an adult from 2700 to 2800 grams daily in food and 

 drink. 



Withdrawal of water increases the disintegration principally of the albu- 

 minous tissues. If thirsting cats are kept for a long time in hot air, a con- 

 centration of the blood becomes manifest, which, through chemical injury, 

 leads to a fatal central narcosis by poisoning of the vital centers. 

 28 



