PROBLEM I. How to Choosc Foods 





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Fig. 199 Above is a pig suffering frov! rickets. 

 Below is the same pig after small daily doses of 

 cod liver oil. What did the oil supply? (Wis- 

 consin AGRICULTURAL EXPERIMENT STATION) 



while heat is appHed. This, too, saves 

 some of the ascorbic acid. Adding soda 

 to boihng vegetables helps to destroy the 

 vitamin. 



Vitamin D. The lack of vitamin D in 

 babies and young children causes rickets, 

 a condition in which the bones and teeth 

 remain soft and there are malformations 

 in the skeleton. Minerals containing cal- 

 cium and phosphorus are needed for 

 strength and rigidity in bones and teeth. 

 But these minerals cannot be used in the 

 body if vitamin D is lacking. Ordinary 

 milk contains both calcium and phos- 

 phorus but has very little vitamin D. In 

 fact, no natural food, even of the many 

 foods eaten by adults, contains very much 

 vitamin D. 



But we have learned two important 



Wisely 1 8 1 



facts in recent years about vitamin D. 

 In the first place, fish oils such as halibut- 

 liver oil and cod-liver oil are excellent 

 sources of this vitamin. Thev are often 

 given particularly to babies to supply the 

 much needed vitamin D. In the second 

 place, many plant foods contain a sub- 

 stance {ergosterol) which turns into vi- 

 tamin D in the presence of the ultraviolet 

 rays of the sun. Many animal tissues 

 contain a similar substance {cholesterol). 



Both plant and animal foods can be 

 exposed to ultraviolet light for the pro- 

 duction of vitamin D. Such exposure to 

 ultraviolet light is called irradiation 

 (ir-ray-dee-a'shun). Milk is often so 

 treated in fresh or evaporated form. 

 Bread is sometimes irradiated and so are 

 some of the cereals. But not all irradia- 

 tion is successful. Sometimes fish-liver 

 oils or yeast are irradiated and fed to 

 cows which then produce milk richer 

 in vitamin D. 



We, being animals, contain this same 

 substance (cholesterol) which can be 

 turned into vitamin D. In the bright 

 sunshine, which contains ultraviolet light, 

 we are constantly making this vitamin. 

 That is why vitamin D is called the "sun- 

 shine vitamin," although, of course, sun- 

 shine contains no vitamin. Many people, 

 however, do not get enough sunshine. 

 The ultraviolet rays do not pass through 

 ordinary window glass. And those of us 

 who live in cities, particularly smoky 

 cities, and in climates with a long winter 

 season, lack the sunshine we need for 

 making vitamin D. 



Vitamin D seems to be a vitamin of 

 which you can get too much. Vitamin 

 A, if taken in excess of one's needs, ac- 

 cumulates and can be used at a later time; 



