542 A MANUAL OF PHYSIOLOGY 



within narrow limits. In hunger the organism clings to its 

 inorganic materials, as it clings to its tissue-proteins ; 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 proteins are excreted, so that 

 a starving animal never dies for want of salts. 



When sodium chloride is omitted as an addition to the food 

 of man, the decomposition of protein seems to be slightly acceler- 

 ated, but for a time, at least, there are no serious symptoms 

 (Belli). The Hereros in Damaraland, who are physically one 

 of the finest races in Africa, are said not to use salt (Reclus). 

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

 possible artificially freed 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 particularly 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 concerned in movement scarcely suffer 

 at all (E. Voit). 



It is not indifferent in what form the calcium is taken, nor can it 

 be replaced to any great extent by other earthy bases, as magnesium 

 or strontium. Weiske fed five young rabbits of the same litter on 

 oats, a food relatively poor in calcium. One of the rabbits received 

 in addition calcium carbonate, another calcium sulphate, a third 

 magnesium carbonate, and a fourth strontium carbonate. At the 

 end of a certain time it was found that the skeleton of the rabbit fed 

 with calcium carbonate was the heaviest and strongest of all, and 

 contained the greatest proportion of mineral matter. Then came 

 the rabbit fed with calcium sulphate. The animal which received 

 only oats had the worst-developed skeleton ; the condition of the 

 animals fed with magnesium and strontium carbonates was but little 

 better. 



Milk is a food rich in calcium arid also in phosphorus, a cir- 

 cumstance evidently related to the rapid development of the 

 skeleton in the young child. As in the other natural foods, the 

 alcium and phosphorus are partly in the form of organic com- 

 pounds, united with the proteins, the calcium especially with 

 caseinogen, and partly in the form of inorganic salts. Both of 

 these elements are more easily assimilated by the body in the 



