ANIMAL LIFE AND ANIMAL PRODUCTS. FOODS 437 



through deficiency in vitamins. These are substances present 

 in minute quantities in most fresh or unsterilized foods, particu- 

 larly in milk and green vegetables, without the aid of which cer- 

 tain parts of the animal mechanism either cease to develop or 

 fail to perform their functions entirely. The three known types 

 are: 



(1) Fat-soluble vitamin A, plentiful in milk, butter, the yolks 

 of eggs, cod-liver oil and the leaves of green plants, but not found 

 in grains, sugars, or refined vegetable fats and oils. This vitamin 

 is needed to promote the growth of children; its absence leads to 

 rickets and a disease of the eye called xerophthalmia. 



(2) Water-soluble vitamin B, plentiful in the outer hull of 

 grains, beans, green leaves and fruit and yeast, but not in the 

 kernels of grains, such as polished or milled rice. Deficiency of 

 this vitamin in the diet leads to boils and skin eruptions, and in 

 extreme instances to beriberi. 



(3) Water-soluble vitamin C, plentiful in citrous fruits, to- 

 matoes, cabbage, lettuce and other fresh fruits and vegetables. 

 The value of this vitamin lies in the prevention and cure of 

 scurvy. It is easily destroyed, except in the case of acid foods, 

 by heating, drying or ageing. Since milk is neutral, infants fed 

 entirely on pasteurized milk are almost sure to develop a mild 

 case of scurvy unless the diet also includes a little orange juice 

 or some other source of water-soluble vitamin C. Owing to the 

 acid nature of tomatoes, even the canned product is rich in this 

 vitamin. A knowledge of this fact was put to good use by the 

 authorities of the British armies in Mesopotamia and Palestine 

 during the war, when fresh fruits and vegetables were unobtain- 

 able. 



Animal Products. Many valuable products, apart from 

 foods, are derived from animal life. The use of animal products 

 in fertilizers (calcium phosphate from bones, nitrogen compounds 

 from manure, etc.) has already been discussed (Chapter XXXV). 



