METABOLISM DURING STARVATION 335 



diet. Depriving an animal of water will kill it more quickly than 

 depriving it of the dry proximate principles of the food. 



Water is taken in as such and in combination with the food. Fresh 

 fruit and vegetables have a large water content. This water may be 

 contained in the system of water-tubes of a plant, when it is more or 

 less pure water, or it may be in the form of " sap," when it is more 

 concentrated and contains mineral salts and organic bodies in addition. 

 Lean meat contains about 80 per cent, of water, so a carnivore almost 

 gets enough water in its food. 



The proportion of water in various vegetables can be seen in the 

 table on p. 349. 



Lack of Mineral Salts. The withholding of mineral salts from the 

 diet also brings about death more quickly than the withholding of 

 the proximate principles. The salts of the body are partly in solution 

 and partly combined with the organic substances. Those in solution 

 are of the greatest importance in providing the proper medium for 

 the living tissues. When salts are withheld, those cqmbined with the 

 organic substances of the body become free to replace the salts in 

 solution, which are lost in the urine. 



The ions of sodium, potassium, and calcium, must be continually 

 taken in with the food, to keep the proper relationship between these 

 bases in the blood, so that the action of the ion of no one base pre- 

 dominates. We know that certain enzymic processes, such as the 

 clotting of blood and milk, depend on the presence of calcium ions, 

 and that muscular contraction is affected by the concentration of 

 calcium, sodium, and potassium ions present in the blood. When 

 calcium is withheld from the diet, the bones are gradually decomposed 

 to replace the loss. 



Different results follow the withholding of one or other groups 

 of salts. Thus, deprivation of chlorides is followed by marked symp- 

 toms of inanition. This is due partly to gastric disturbance, and 

 partly to the ascendancy obtained by the potassium ion, which works 

 deleteriously upon the bodily functions. When there is a lack of 

 sodium salts as compared with potassium salts, or an abundance of 

 potassium salts relative to sodium salts, such as occurs with a vegetable 

 diet, the potassium of the salts ingested is in part replaced by sodium 

 from the body, and some of the sodium salt so formed is excreted in 

 the urine. This causes a loss of NaCl from the body, and a supply 

 of NaCl becomes imperative. For this reason many vegetarian 

 animals wander miles to visit " salt-licks " lumps of crude rock salt. 

 On an animal diet sufficient salts are introduced with the food itself. 

 The desire for salt by the various human races varies with the pre- 

 ponderance of vegetable food in their diet. The peasants in France eat 

 four times as much salt as the town dwellers; the carnivorous tribes 

 of men do not know or do not value salt. Rice-eaters are an exception. 

 Rice contains six times less potassium than wheat, ten to twenty 

 times less than peas, twenty to thirty times less than potatoes. Rice- 

 eaters, like flesh-eaters, do not require much common salt. In the 

 Soudan the negroes burn a plant which yields an ash rich in sodium, 



