STATISTICS OF NUTRITION 621 



are more or less intimately united to the proteins of the tissues and 

 juices, some simply dissolved in the latter. The chlorides, phos- 

 phates 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 pre- 

 dominate in the bones. The amount and composition of the ash 

 of each organ only change 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 accelerated, 

 but for a time, at least, there are no serious symptoms (Belli). 



It is a general rule that purely carnivorous animals do not desire 

 salt, and the same is true of human beings living on a purely animal 

 diet, while vegetable feeders eagerly seek it. On the other hand, 

 when an animal, even a carnivore, 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 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 mag- 

 nesium 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 as a Food. Milk is a food rich in calcium and also in phos- 

 phorus, a circumstance evidently related to the rapid development 



