86 THE FEEDING OF ANIMALS 



believed to be due to the reaction of certain food sub- 

 stances on the inner membranes of the stomach. 



Vitamines, or food accessories, are regarded as being 

 attached to foods, and may properly be styled growth- 

 promoting substances. These bodies of an unknown 

 nature seem to fall into two classes (Hart and McCollum), 

 the fat-soluble accessory attached to butter fat, egg yolk 

 fat, pig kidney fat, and certain vegetable fats, and a 

 water-soluble accessory attached to the wheat embryo, 

 egg yolk, milk-powder, and other foods. These accessories 

 are not destroyed by heat, even when subjected to the 

 action of steam for two and one-half hours. The fat 

 soluble accessory may be concentrated in butter oil by 

 fractional crystallization of the harder fats. 



