112 PRINCIPLES OF ANIMAL BIOLOGY 



Rickets, the imperfect growth of bones and teeth, is caused by a 

 deficiency of vitamin D. This substance is now known to be calciferol 

 (C28H44O). It is produced from a closely related substance, ergosterol, 

 regularly present in the skin, by ultraviolet radiation. In summer time 

 the conversion of ergosterol to calciferol is usually adequate in most 

 regions, but in winter it is often advisable to supply vitamin D artificially. 

 The common foods containing it are butter, milk, and the oils of liver and 

 other animal tissues. So well understood are the preventive properties 

 of these foods, or the manufactured vitamin, that rickets, once a common 

 disease, is seldom observed in most communities. 



Reproductive disturbances in some animals are caused by lack of 

 vitamin E, a-tocopherol (C29H50O2). In its absence female rats do not 

 retain the embryos in the uterus, and male rats do not produce functional 

 spermatozoa. No such effects have yet been shown in man. Vitamin E 

 occurs widely in plant and animal oils, particularly in the germ of wheat. 



Failure of coagulation of the blood may be caused by lack of vitamin 

 K, whose formula is C31H46O2. In its absence the body does not pro- 

 duce enough prothrombase, from which the clotting enzyme is produced 

 at wounds. Vitamin K is regularly administered before child-birth, with 

 a considerable decrease in mortality from bleeding in both the newborn 

 children and their mothers. Natural food sources of the vitamin are 

 leafy vegetables; it is prepared commercially from alfalfa. 



Vitamin P, not yet identified chemically, is closely related to ascorbic 

 acid (C) and is involved in scurvylike weakness of the walls of blood 

 capillaries. Its status is still unsettled. 



The necessary amounts of vitamins are so small (0.01 gram or less 

 daily) that they cannot be regarded as sources of energy. They must 

 be in some way essential in protoplasmic structure. Three of the 

 vitamins, thiamin, riboflavin, and the antipellagra factor, are known to 

 enter the composition of important oxidative enzymes; that is, they 

 furnish the nonprotein part of the enzymes. What other structural 

 contributions the vitamins make is not known. 



The need of vitamins in food differs greatly in different animals. 

 Rats, for example, need no ascorbic acid in their diet, since they syn- 

 thesize it in their metabolism; rats never have scurvy. Man can get 

 along with little or no thiamin in his diet; but bacteria in his large 

 intestine must then supply it. As stated above, man probably does not 

 require vitamin E, or else produces it in normal metabolism. 



References 

 Carlson, A. J., and V. Johnson. The Machinery of the Body. University of 



Chicago Press. (Chap. VII.) 

 Mitchell, P. H. A Textbook of Ceneral Physiology. 3d Kd. McGraw-Hill Book 



Company, Inc. (Chap. XVIII, digestion; Chap. XXI, respiration; pp. 745-772, 



vitamins.) , 



