METABOLISM AND FOOD 93 



stuff. In Tables I and III of the Appendix the 

 amount of digestible protein in the food is also given. 

 It must not be forgotten though that the starch value 

 also includes the effect which the protein has in 

 common with the starch. It would not be correct 

 to include only nitrogen-free substances in the 

 starch equivalent, for in very many cases the greater 

 part of the food protein is not used for the forma- 

 tion of flesh, but utilised in the same way as the 

 nitrogen-free nutrients . 



(h) The effect of mineral substances. 



When an animal is burnt, ash is left which con- 

 tains, as does the ash of the plant, potash, soda, 

 lime, magnesia, oxide of iron, phosphoric and sul- 

 phuric acids, chlorine, etc. These materials are not 

 unimportant, but are an absolute necessity, as has 

 been proved by experiments in which food lacking 

 in them was given. It was found that under these 

 conditions the animals constantly lost mineral 

 substances, such as phosphoric acid and lime; in 

 one case lambs were found to lose 0-5 gr. phosphoric 

 acid and 1-2 gr. of lime per head per day. If 

 feeding with food poor in mineral substances is 

 continued for some length of time, appearances of 

 disease are to be seen in consequence of the loss of 

 mineral substances from the body. The symptoms 

 as a rule are great weakness in the legs, trembling 



