586 METABOLISM 



being present in most animal fats, but not in all; for example, it is 

 absent from the fat surrounding the pig's heart. By using such a 

 nomenclature it is recognized that the subject is as yet only in an early 

 state of development. 



We may sum up the main facts of this chapter by stating that growth 

 and maintenance are more than a mere problem of energy supply. 

 Granted that this is sufficient, we must also have a suitable admixture of 

 building units of protein and the presence of extremely small quantities 1 

 of some unknown accessory substances. These are present in some natural 

 foods but not in others, and some are soluble in water and others in fats. 

 They are found, for example, in animal fats but not in those of vegetable 

 origin. Both fat- and water-soluble factors are present in large quanti- 

 ties in milk. 



Both accessory food factors are necessary, as is illustrated in the fol- 

 lowing summary of experiments from Lusk's " Science of Nutrition," 

 (third edition). 



Purified protein + carbohydrate + vegetable fat + inorganic salts = no growth. 

 " + + butter fat *.'*'' " no growth. 



" " + " + vegetable fat + ", " +vitamines (accessory 



factor B) = no growth. 

 + " + butter fat + " " + vitamines = growth. 



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. 



The practical application of the results of these numerous and at 

 present somewhat bewildering observations to the nutrition of man, 

 and particularly to the dietetic treatment of disease, is undoubtedly 

 very great. This is especially so in infants and growing children, in 

 whom the correction of some slight inadequacy in the diet may have 

 the most pronounced results, not only on growth and nourishment, but 

 also on the power of resistance against disease and infection. The bene- 

 ficial influence of cod-liver oil, for example, may depend on some fat- 



