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measured amounts of pure carbohy- 

 drates, proteins, fats, minerals, and water. 

 By using the prepared substances instead 

 of ordinary foods they were able to con- 

 trol the amounts more accurately. To 

 their astonishment the rats developed an 

 eye disease, sickened, and died. 



The experiment was repeated but this 

 time as soon as the rats became sick some 

 of them were given small amounts of 

 raw milk each day in addition to their 

 regular diet. These rats regained their 

 health and remained normal. It was plain 

 that rats needed something more than 

 proteins, fats, carbohydrates, minerals, 

 and water. Although the experimenters 

 did not know what that substance M'as, 

 the experiment indicated that it was con- 

 tained in raw milk. Also, it was apparent 

 that the substance was needed in small 

 amounts only. It was concluded that this 

 substance was a vitamin and it was given 

 the name of vitamin A. 



In the meantime others had discovered 

 by experiment that the citrus fruits like 

 oranges and limes contain a vitamin which 

 prevents scurvy. This vitamin was called 

 vitamin C. 



Beriberi, scurvy, and the eye disease 

 caused by lack of vitamin A are called 

 deficie?jcy diseases. 



The importance of vitamins. These ex- 

 periments definitely established the pres- 

 ence of tiny amounts of important sub- 

 stances in our foods besides the well- 

 known food substances. There followed 

 a vast amount of experimentation which 

 still continues. Important discoveries fol- 

 lowed one another in close succession. 

 We now know of about a do7xn vitamins 

 necessary to our good health and our 

 general well being. By the time you read 



How a Co?fiplex Aimjial Uses Food unit iv 

 this others may have been added to the 



list. All of us must know the following 

 about each vitamin: the foods in which 

 it occurs; how we are affected by insuf- 

 ficient amounts of it; and to what extent 

 cooking or the aging of the food destroys 

 it. By applying this information we may 

 hope to keep ourselves much more fit. 

 Most of us are not likely to become af- 

 flicted with beriberi, scurvy, or the eye 

 disease described above because most of 

 us eat a variety of foods. In any normal, 

 fairly varied diet at least small amounts 

 of the necessary vitamins are almost sure 

 to appear. Our problem is to get the full 

 amount of each vitamin needed to keep 

 us in the best of health. 



Vitamin A. Vitamin A is one of the 

 vitamins that can now be made in the 

 laboratory. It is composed of the same 

 three elements as carbohydrates (C,H,0). 

 In animals vitamin A is made in the liver. 

 But it can be made only if carotene 

 (care'o-teen) is present. Carotene is a 

 yellow substance found not only in car- 

 rots and other yellow vegetables and 

 fruits, but also in the green parts of all 

 plants. Vitamin A or the unchanged 

 carotene can accumulate in the liver, in 

 the fatty part of milk, in q^2, yolk, in 

 kidneys, and in the pancreas. h\\ of these 

 foods are, therefore, good sources of 

 vitamin A. And since your liver can make 

 vitamin A out of carotene, you can also 

 be sure of getting your supply of the 

 vitamin by eating yellow and green plant 

 foods. In spite of the many foods that 

 supply vitamin A, many people suffer 

 from a slight deficiency of it. 



You read above that in rats, a defi- 

 ciency of vitamin A resulted in a serious 

 eye disease. In man, too, a serious vitamin 



