VITAMINS 355 



oranges, peaches, tomatoes, allalla, aiul pumpkins are good soLUxes 

 of carotene. Yellow corn is the only cereal containing significant 

 amounts. Eggs, liver and fish-liver oils are high in vitamin A, while 

 milk and butter are rich in both carotene and vitamin A. It is now 

 customary to fortify many foods with one or the other factor, especially 

 oleomargarine and shortenings. Vitamin A is relatively unstable in air 

 unless protected by natural or added antioxidants, including vita- 

 min E. 



Deficiency 



Severe deficiency symptoms occur in adult animals only after pro- 

 longed deprivation. Human beings previously on good diets show 

 little effect after 1 to 2 years without carotene or vitamin A because 

 of the supply stored in the liver. Shortages in the diets of very young 

 animals produce rather rapid and severe symptoms. Starting first with 

 night blindness, other malfunctions appear, including poor growth, 

 kidney stones, reproductive failures, degeneration of nerve tissues, 

 abnormal bone growth, degeneration of epithelial tissues followed by 

 secondary infections, and characteristic drying and destruction of the 

 cornea, leading to blindness. Rather complete recoveries are common 

 if treatment is administered in time. Night blindness always seems 

 to be the earliest change, potentially a serious matter where the 

 victim drives a car, especially since he is never conscious of his dis- 

 ability. 



Deficiencies are probably rare in people of western countries at 

 present but were encountered in significant numbers until the end of 

 World War I. Danish children suffered especially because of export 

 of the dairy products to Germany. Lack of vitamin A is still the chief 

 cause of blindness in children in India, China, and southeast Asia, 

 where the cases are nimierous and two-thirds result in blindness. 



Repeated great overdosage with vitamin A can cause fragility of the 

 bones or swelling and soreness in rats. Doses of 500,000 imits daily 

 for extended periods to infants have produced moderate symptoms. 

 Illness and even death have been reported in Arctic exploring parties 

 as a result of the consumption of polar bear liver, an extremely con- 

 centrated source of Vitamin A. 



VITAMIN D 

 Chemistry 



A number of related compoimds possess vitamin D activity in the 

 prevention and cure of rickets. Of these only two are of much prac- 



