390 TEXTBOOK OF ZOOLOGY 



5. Pantothenic aeid (CgHiTOgN). 



(a) Sources: Liver, milk, egg yolk, yeast, molasses, peanuts. 



(b) Functions: Essential for growth. 



(c) Effects of deficiency: Graying in black rats. Dermatitis in rats and 

 chickens. 



6. Biotin (doHieOsNjS). 



(a) Sources: Egg yolk, yeast, cereal grains, molasses. 



(b) Functions: Essential for growth. 



(c) Effects of deficiency: Thickening of skin and dermatitis in clucks 

 and rats. 



III. Vitamin C or Ascorbic Acid (CoHsOe) — antiscorbutic-water-soluble. 



(a) Sources: Citrus fruits, tomatoes, turnips (most mammals except pri- 

 mates and guinea pig can synthesize this vitamin). 



(b) Functions: Maintains structure of capillary walls. 



(c) Effects of deficiency: Scurvy in human and guinea pig (bleeding in 

 mucous membranes, beneath skin and into joints). 



IV. Vitamin D (C2SH44O) — antirachitic. 



(a) Sources: Tuna and cod-fish liver oils. Exposure of skin to ultra- 

 violet radiation. 



(b) Functions: Eegulation of calcium and phosphorus metabolism. Ke- 

 quired for normal growth and mineralization of bone. 



(c) Effects of deficiency: Soft, deformed bones in young (rickets). Soft 

 bones (osteomalacia) especially in women of the orient. 



V. Vitamin E or Tocopherol (CjaHjoO.)- — antisterility. 



(a) Sources: Wheat germ oil, green leaves, other vegetable fats. 



(b) Functions: Promotes rapid cell proliferation and differentiation. 



(c) Effects of deficiency: Sterility in male fowls and rats. Failure of 

 spermatogenesis. Death of rat embryos in uterus. 



VI. Vitamin K (C3,H4e02) — antihemorrhagic. 



(a) Sources: Green leaves, alfalfa, also certain bacteria of the "intesti- 

 nal flora." 



(b) Functions: Influences the production of prothrombin by the liver 

 (prothrombin is necessary for blood clotting). 



(c) Effects of deficiency: Blood fails to clot. 



The Respiratory System.— The respiratory system is at least in 

 part an outgrowth of the digestive canal. In most aquatic verte- 

 brates respiration is accomplished by drawing water through gill 

 slits in the wall of the pharynx. Air-breathing, terrestrial forms 

 have developed the trachea (windpipe) and lungs as another out- 

 growth of the pharynx. A certain amount of respiration takes place 

 through the skin. The respiratory process is composed of two 

 phases: exterTial respiration which includes the exchange of the 

 gases, oxygen and carbon dioxide, between the external environ- 

 mental medium and the blood ; and internal respiration which is the 



