94 SCIENTIFIC FEEDING OF ANIMALS 



of the muscles, cramp, and excitability, whilst 

 death follows sooner than if the animal had had no 

 food at all. The mineral substances of the body 

 undergo metabolism just as do the protein and fat, 

 only to a less extent, for they are a necessary part 

 of the organism, and must be given to growing 

 animals, whose organs are increasing, in larger 

 quantities than when growth has ceased. As to 

 the exact part which the various mineral substances 

 play there is not yet any very exact knowledge. 

 The following are the most important facts known — 

 (a) Potash and soda. — Potassium is found princi- 

 pally in the cell walls, muscles, and blood corpuscles. 

 Sodium, on the other hand, in the blood, lymph, 

 saliva, gastric juice, etc. The value of potassium for 

 the changes which take place in the body is not yet 

 known, but sodium combined with chlorine is present 

 as common salt, and there are indications that it 

 prevents swelling up of the cells, assists the passage 

 of many substances through the cells, dissolves 

 some proteins, and forms hydrochloric acid and 

 soda in the digestive juices. When salt is taken in 

 moderate quantities it appears to favour the putting 

 on of flesh, but in excess it increases the quantity of 

 water drunk, and causes all those drawbacks which 

 are associated with a too liberal consumption of 

 water (p. 101). The ordinary feeding-stuffs and 

 drinking-water contain, as a rule, so much sodium 

 and chlorine that if no salt is given the vital functions 



