618 METABOLISM 



addition of the ash of the lipoid extract failed to maintain the mice, so 

 that the lacking substance could not be inorganic in nature. 



As we shall see immediately, these results are dependent upon the 

 presence in fats of so-called accessory food factors or vitamines. 



The Relationship of Inorganic Salts. Inorganic salts are also an es- 

 sential ingredient of the diet. McCollum found that young animals soon 

 ceased to grow when fed on a diet of corn and purified casein, but that 

 rapid growth returned when a suitable salt mixture was added. Oats, 

 wheat, and beans have also been shown to require some adjustment of their 

 ash content to make them adequate for growth. Most of the animal foods 

 contain in themselves sufficient inorganic material, as is evidenced 

 among other things by the adequacy of milk alone as diet for growing 

 animals and the abhorrence of salt that is shown by strictly carnivorous 

 animals. In the usual mixed diet of man there is almost always enough 

 inorganic material, the salt which he adds being largely for seasoning 

 purposes. When a preponderance of vegetable food is taken, however, 

 the salt comes to have a real dietetic value. 



ACCESSORY FOOD FACTORS, VITAMINS 



Even when the requirements of the animal body for calories and 

 protein building stones are fully met, the diet will fail to maintain 

 health unless it also contains substances of an unknown chemical nature 

 called "accessory food factors" or "vitamins." These are entirely of 

 plant origin, and require to be taken only in very small quantities to 

 display their beneficial action. They do not become rapidly destroyed 

 in metabolism, but may remain attached to the tissues sufficiently long 

 so that carnivorous animals obtain them indirectly. Great advancement 

 in our knowledge of vitamins had been made in recent years, particu- 

 larly through the work of F. Gowland Hopkins and Harriette Chick, 70 

 Osborne and Mendel, 71 Funk, 15 McCollum, 12 and McCarrison. 75 



Serious and prolonged absence of certain vitamins from the dietary 

 may hinder the growth of young animals or may be the cause of various 

 serious diseases in adults. 



The human diseases which are known definitely to be due to the absence 

 of one or other of the vitamins are beriberi, scurvy and rickets, and 

 accordingly three vitamins are distinguished: 



1. Antiberiberi or antineuritic vitamin (also called water soluble "B" 

 growth factor). 



2. Antirachitic vitamin (also called fat-soluble A growth factor). 



3. Antiscorbutic vitamin. 



It will be observed that the vitamins also differ from one another in 

 their solubilities. 





