J 50 Comparative Animal Physiology 



substitute quantitatively for choline in the diet of the roach. ^^^ Choline is 

 not required in the diet of the ciliate T etrahymena?'^ 



Inositol also is a constituent of many lipids, occurs in nucleic acids, and is 

 widely synthesized. Certain strains of microorganisms require it, but no in- 

 sects have been found to need it in the diet. Inadequate amounts may be 

 synthesized by growing chickens and turkeys and by mammals if the diet 

 contains the cereal product phytin;'-'-' ^^-^ under these conditions it is a 

 dietary essential. Early reports of specific effects of inositol on some types of 

 alopecia (hair loss) appear not to have been confirmed. 



Para-aminobenzoic acid is apparently a precursor of folic acid and may not 

 be a true dietary factor for animals if there is an adequate supply of folic acid. 

 Additions of p-aminobenzoic acid favor survival in vitro of Plasmodium 

 knoivlesii, ^-^^ but it apparently is not needed by insects or higher animals. 



Ascorbic Acid (Vitamin C). Ascorbic acid has the following structure: 



This is a substance which is readily oxidized, and therefore it may be important 

 in maintaining a proper oxidation-reduction balance in many cells. It is widely 

 distributed in animal tissues and in many plant sources and appears to decrease 

 in the adrenal cortex under various stress conditions, as indicated for tempera- 

 ture extremes in Chapter 10, p. 349. Ascorbic acid was early discovered as the 

 anti-scurvy vitamin in man. Its lack results in small scattered hemorrhages 

 and lesions, particularly of the gums. Ascorbic acid is needed in the production 

 of intercellular cement, particularly of capillaries. The human requirement is 

 1.6 to 1.7 mg./kg./day. ^-^ Ascorbic acid is not required in the diet by all 

 mammals. It is synthesized in sufficient amounts by the rat and hamster, but 

 must be fed to guinea pigs, monkeys, and men. Ascorbic acid appears not to be 

 essential in the nutrition of insects, but those animals may synthesize it. ^^^ 

 The larvae of honeybees contain more ascorbic acid than do the adults. ^^ It 

 is said to be needed by cultures of the higher trypanosomes (mammalian blood 

 parasites) such as Leishmania and Schizotrypanum, but not by free-living 

 protozoans and primitive trypanosomes such as Strigomonas and Lepto- 

 monas. ^^ 



Vitamin P. This term is applied to a group of products found in green 

 plants and citrus fruits whose action may be more pharmacological than 

 nutritional. These substances, flavone glycosides, rutin, and others, protect 

 against capillary hemorrhages and regulate the capillary cement. They differ 

 from ascorbic acid and may not be true vitamins. 



Purines and Pyrimidines. In some animals purines and pyrimidines are 

 dietary essentials. In culturing the ciliate Tetrahymena Kidder and Dewey 



