GENERAL ZOOLOGY 



aminobenzoic acid (PABA) which is a requirement for the synthesis of foHc 

 acid by some of the pathogenic bacteria. When the sulfa drugs are present, 

 they block the utilization of PABA by the bacteria; folic acid is not syn- 

 thesized, and the bacteria cease to grow. Since animal cells do not use 

 PABA, they are not damaged by the drug. 



Vitamin Bj2 is a unique type of chemical compound, characterized by its 

 complex ring structure and containing one cobalt atom and a single cyanide 

 group; it is known as cyanocobalamin. It was isolated in 1948, subsequently 

 synthesized, and its molecular structure reported in 1955. Vitamin Bj2 is 

 found chiefly in foods of animal origin, where it is present in very low con- 

 centration. Intestinal microorganisms synthesize Bj.,, which can then be 

 absorbed. It has several functions, some in conjunction with folic acid, and 

 participates in a variety of fundamental metabolic reactions. It also has a 

 specific effect on the formation of blood cells and is often called the anti- 

 pernicious anemia vitamin. Injections of Bj^ in patients with pernicious 

 anemia usually produce dramatic relief of the anemia, as well as of the neuro- 

 logical symptoms of the disease. In addition, vitamin Bj2 is essential for the 

 growth of young mammals. 



Another type of water-soluble vitamin is ascorbic acid, vitamin C, or the 

 antiscorbutic vitamin. It appears to be a dietary requirement for only a few 

 animals, but man is one of them. Deficiency of ascorbic acid results in 

 scurvy, characterized by bleeding through capillary walls. The cellular func- 

 tion of ascorbic acid remains unknown, except that it participates in some 

 way in the formation of intercellular material. Citrus fruits and tomatoes 

 are rich sources of this vitamin, and it is abundant in paprika and in the 

 cortex of the adrenal gland. 



In the light of modern investigations on the nutritional requirements of 

 animals, it becomes evident that in order to secure a proper balancing of the 

 diet we must do more than obtain a certain ratio between amounts of carbo- 

 hydrates, lipids, and proteins. It is essential that the proteins contain the 

 amino acids needed by the cells, that the inorganic constituents be present 

 in proper concentrations, and that vitamins be furnished. Abnormal func- 

 tions of the body conditioned by food inadequate in vitamins and minerals are 

 serious factors in human welfare. On the whole, however, the very numerous 

 cases of borderline malnutrition, predisposing the individual to various 

 diseased conditions and allowmg him to maintain only a low level of physical 

 and mental efficiency, are of more importance to society as a whole. Every 

 individual should eat abundantly of the protective foods containing vitamins. 



It is characteristic of the nutrition of animals, with only a few exceptions 

 (p. 242), that they cannot build their foods from the constituent chemical 

 elements but must make use of compounds produced by the cells of other 

 animals or of plants. The products of metabolism of one kind of organism 

 are not ordinarily usable, as such, by another type of organism. Therefore, 

 food, in addition to possessing the necessary qualities which have been dis- 

 cussed, must be utilizable by the animal eating it. The chemical processes 



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