176 ESSENTIALS OF ZOOLOGY 



V. Vitami/n E or Tocopherol (C29H50O2) — 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. 



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VI. Vitamin K (CsiH^gOz) — 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. 



Respiration 



R-espiration has been defined as the process involving the ex- 

 change of gases between the protoplasm of an organism and its en- 

 vironment. All living protoplasm must be provided with a means 

 of receiving oxygen and giving up carbon dioxide. In Protozoa and 

 simple Metazoa, such as sponges, coelenterates, flatworms, round- 

 worms, and even some annelids, this gaseous exchange is made by 

 almost direct diffusion through the cell membranes to the surround- 

 ing medium. This movement of gas through the cell membranes 

 depends on the partial pressure of the particular gas on the two 

 sides of the membrane. Gas will flow in the direction toward the 

 least pressure. 



In the larger and more complex animals where the volume of 

 tissue is such that a more active interchange of gases is required 

 than the general body surface will permit, special organs or modi- 

 fications of the surface must be provided. Also the possibilities of 

 oxygen absorption are greatly increased by the development of 

 respiratory pigments like hemoglobin and hemocyanin, which are 

 carried in a blood vascular system all over the body. These pig- 

 ments readily unite with oxygen to form oxyhemoglobin in the 

 case of the former. Thus the blood is enabled to absorb far more 

 oxygen than an equal quantity of ordinary liquid. When the oxy- 

 gen pressure of the surrounding tissue is sufficiently low, the oxy- 

 hemoglobin releases its oxygen rapidly. Carbon dioxide accumu- 

 lates in excess in the tissues and diffuses from the cells to the 

 lymph, thence to the plasma where much of it combines with sodium 

 as sodium carbonate. Small amounts of CO2 combine with the 

 hemoglobin. 



