METABOLISM, NUTRITION AND DIETETICS 473 



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

 explanat on 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 intimately united to 

 the proteids of the tissues and juices, some simply dissolved 

 in the latter. The chlorides, phosphates and carbonates are 

 the most important ; the potassium salts belong especially to 

 the organized tissue elements, the sodium salts to the liquids 

 of the body ; calcium phosphate and carbonate predomi- 

 nate in the bones. The amount and composition of the 

 ash of each organ only changes within narrow limits. In 

 hunger the organism clings to its inorganic materials, as 

 it clings to its proteids ; the former are just as essential 

 to life as the latter. In a starving animal chlorine almost 

 disappears from the urine at a time when there is still much 

 chlorine in the body ; only the inorganic salts which have 

 been united to the used-up proteids are excreted, so that a 

 starving animal never dies for want of salts. 



On the other hand, when an animal is fed with a diet as 

 far as possible free from salts, but otherwise sufficient, it 

 dies of salt-hunger. The blood first loses inorganic material, 

 then the organs. The total loss is very small in proportion 

 to the quantity still retained in the body ; but it is sufficient 

 to cause the death of a pigeon in three weeks, and of a dog 

 in six, with marked symptoms of muscular and nervous 

 weakness. A deficiency of lime salts causes changes par- 

 ticularly in the skeleton, although the nutrition of the rest 

 of the body is also interfered with. These changes are of 

 course most marked in young animals, in which the bones 

 are growing rapidly. In pigeons on a diet containing very 

 little calcium the bones of the skull and the sternum become 

 extremely thin and riddled with holes, while the bones con- 

 cerned in movement scarcely suffer at all (E. Voit). 



