FUNCTIONS OF THE NUTRIENTS 195 



that pelagra, prevalent in the South where the diet of 

 many individuals is considerably restricted, is due to the 

 absence or insufficient supply of one or both of these 

 classes. 



These accessory substances appear to be abundant in 

 egg, milk, and the forage portion of many plants. Fat- - 

 soluble A being deficient in the body fats of animals and 

 absent from the fats or oils of many species of plants. 

 The knowledge of the presence or absence of these growth- 

 promoting substances in cattle foods will undoubtedly be 

 enlarged as investigation proceeds. 



It is shown in experiments by Hart and McCollum 

 that when the rations of animals were restricted to a single 

 plant, that the wheat germ contains a toxic body. Ani- 

 mals fed wholly on the corn plant or its products developed 

 normally and produced young. Those fed on the wheat 

 plant or its products, without the addition of other food, 

 failed to make satisfactory growth and to produce vigor- 

 ous yoimg. Similar results were obtained with wheat 

 products when fed to swine. Such results with the wheat 

 plant were evidently not due to a lack of nutrients but 

 investigation showed that the operating cause was a 

 poisonous principle located in the fat of the wheat, this 

 principle being removed when the wheat oil was extracted. 

 We have here, then, an example of a toxic body con- 

 tained in one of the most common of our feeding-stuffs, 

 the effect of which has been less observed because wheat 

 by-products have constituted only a portion of the food 

 of the animal. 



279. Relation of production values to profit from 

 feeding animals.— The production from a given quantity 

 of food varies greatly under unlike conditions. It can 

 scarcely be doubted that the proportion of the available 



