524 



COLLEGE ZOOLOGY 



381), especially in young children. It is due 

 to the absence in the food of sufficient 

 amounts of certain organic compounds 

 known as sterols. When a sterol obtained 

 from yeast has been treated with ultraviolet 

 radiation, it is known as calciferol and sold 

 under the trade name of viosterol. A sterol 

 occurs in the skin which is transformed into 

 vitamin D when exposed to ultraviolet light. 

 On this account sunlight is a preventive of 

 rickets. Vitamin D also is present in fish- 

 liver oils, eggs, enriched flour, and vitamin 

 D milk. Too much vitamin D may result 

 in harmful effects such as calcifications in 

 the kidneys. 



Vitamin E (Antisterility Vitamin 

 —Tocopherol— C29H50O2) 



This vitamin is necessary for normal re- 

 production in some experimental animals 

 such as rats, mice, and poultry. However, 

 experiments have shown that goats, sheep, 

 and rabbits have a normal reproductive ca- 

 pacity when on a diet deficient in vitamin E. 

 These results should be a warning against 

 the danger of making broad generalizations 

 from experiments on one type of animal. 

 This vitamin is so widely distributed in the 

 foods used by man, such as green leaves and 

 vegetable fats, that there appears to be no 

 reason for concern about it. This vitamin is 

 an antioxidant, which preserves easily oxidiz- 

 able vitamins and fatty acids in foods, or in 

 the body. 



It has also been demonstrated that vita- 

 min E deficiency may result in weakness and 

 even degeneration of skeletal muscles. Mus- 

 cles of animals deficient in this vitamin use 

 oxygen at a much higher rate than normal. 



Vitamin K (Antihemorrhagic 

 Vitamin— C31H46O2) 



Deficiency of this vitamin is responsible 

 for excessive bleeding due to delay in the 

 clotting time of the blood. It is necessary 

 for the formation of prothrombin, one of 



the substances essential for the clotting of 

 blood. It appears that only under extraor- 

 dinary circumstances does man suffer from a 

 deficiency of this vitamin. Bile salts are 

 necessary for absorption of vitamin K in the 

 intestine. In cases of jaundice, due to the ob- 

 struction of a duct so that bile does not 

 flow into the intestine, treatment with bile 

 salts plus vitamin K is found to decrease 

 the bleeding which usually occurs in this 

 disease. It is also the custom to give this 

 vitamin by injection or by mouth, accom- 

 panied by bile salts before operating on a 

 patient with obstructive jaundice. Further- 

 more, treatment of a newborn baby with 

 this vitamin prevents the tendency to bleed, 

 which often exists. The chief sources of 

 vitamin K are green leafy vegetables, and 

 certain bacteria such as those of the intes- 

 tinal flora. 



Only some of the better-known vitamins 

 and for the most part those that are of 

 demonstrated importance in human nutri- 

 tion are mentioned here. Investigations on 

 vitamins are extremely numerous, and new 

 discoveries are frequently announced. 



ABSORPTION 



Water, mineral salts, and digested food 

 must be absorbed from the cavity of the 

 digestive tract and pass into the circulating 

 fluids, then be distributed to the tissues of 

 the body before they can take part in cel- 

 lular metabolism. Very little absorption 

 takes place in the stomach, although alcohol 

 is readily absorbed from it. Some water is 

 absorbed by osmosis from the small intes- 

 tine, but most of the water is absorbed in 

 the large intestine. Inorganic salts diffuse 

 through the intestinal wall, but some other 

 cellular activity is also involved. The prod- 

 ucts of protein digestion (amino acids) are 

 absorbed through the intestinal wall di- 

 rectly into the blood stream. However, glu- 

 cose must first be changed at the cell sur- 

 face into glucose phosphate; this is quickly 

 absorbed by the cells lining the small in- 



