MAlSrUAL OF CATTLE-FEEDINCI. 21 



substances in tlie various tissues and fluids, while it is very 

 constant, is relatively small, except in the case of the 

 bones, but they are absolutely essential constituents of all 

 those parts of the body in which the vital processes are 

 most actively carried on, and in which, consequently, de- 

 composition and rebuilding are continually taking place. 

 As a consequ<5nce, they are continually excreted from the 

 body in considerable quantities with the final products of 

 the metamorphosis of tissue, and the vital processes would 

 soon suffer important disturbances were not a continual^ 

 almost daily, supply provided. 



Salt-hninger, — Numerous experiments have shown that 

 when animals are fed on food from which the mineral 

 matters (salts) have been extracted as completely as pos- 

 sible, they become sleepy, weak, especially in the extremis 

 ties, and finally die iicmx lack of miuei^al food, although 

 the quantity of organic food eaten and dig^ted jnay be 

 amply sufficient to sustain life. 



As an example of these may be i(ientioned some experi- 

 nxents niade at the Physiological Institute of the Univer- 

 sity of Munich, by Forster,* on pigeons and dogs. 



The pigeons were fed with starch and casein, made as 

 free from ash as possible ; the dogs with meat repeatedly 

 extracted with water (to remove the mineral matters) and 

 with fat, sometimes with addition of starch. The results 

 were the same in every case. All the animals became, 

 after a few days, in consequence of " salt-hunger," dull and 

 inactive ; a rapidly increasing weakness of the muscles ap- 

 peared, particularly in the extremities, and toward the end 

 of the experiment cramps and shivering showed a great 

 irritability of the nervous system. 



*Zeitsolir. f. Biologie, IX., 397. 



