174 ESSENTIALS OF ZOOLOGY 



in the muscles to be reconverted into dextrose for oxidation by the 

 tissues as needed. Normally there is a constant supply of dextrose 

 (0.1 to 0.15 per cent) in the blood and this level must be maintained. 

 The final oxidation products of carbohydrates in the body are heat, 

 kinetic energy, water, and carbon dioxide. The last two are dis- 

 charged from the body as waste products. Fat is converted to dex- 

 trose and oxidized to produce heat and kinetic energy. It is usually 

 stored as a reserve fuel supply in adipose tissue over the body. Car- 

 bohydrates in excess may be converted to fat, and stored. 



Vitamins and Their Functions 



Besides proteins, carbohydrates, fats, inorganic salts, and water 

 there is another indispensable class of food material, the vitamins. 

 They are natural substances found in . relatively 'small quantities in a 

 number of different foods. In general, their function is related to the 

 regulation of certain phases of metabolism. They are recognized usu- 

 ally through the abnormal condition brought on by their deficiency. 

 There is little danger of vitamin deficiency for adults living on a bal- 

 anced and mixed diet. Much of our knowledge concerning the symp- 

 toms brought on by lack of different substances has been gained by 

 feeding experiments on different kinds of laboratory animals. This 

 information is then applied to human beings. The following outline 

 summarizes the essential points concerning vitamins. 



The Vitamins and Their Characteristics 



I. Vitamiji A (C20H30O) — antixerophthalmic — fat soluble. 



(a) Sources: carotene (C40H56) a yellow pigment in green plant leaves, 

 carrots, and such plant tissues. Transformation of this pigment into 

 the vitamin which is especially stored in shark, cod, halibut or other 

 fish liver oil, egg yolk, and milk. 



(b) Functions: Influences efficiency and acuity of vision, important fac- 

 tor in regeneration of visual purple of retina, strengthens and pro- 

 motes hardiness in epithelial tissue. 



(c) Effects of Deficiency: Xerophthalmia (lack of tear secretion and dry 

 cornea), and ''night blindness" in human. ''Nutritional" roup in 

 birds. 



II. Vitamin B* "Complex." 



1. Bi or Thiamin (C12HJ7ON4S) — Antineuritic. 



(a) Sources: Germ of wheat and other cereal grains, peanuts, liver, and 

 egg yolk. 



♦There are still other recently discovered fractions of Vitamin B, whose func- 

 tions are specific. 



