132 Comparative Animal Physiology 



The rat converts carotene to vitamin A, probably in the small intestine. 

 Carotene is converted slowly and is stored in the liver as Ai in codfish'"- ^-" 

 and lobster, ^'^^ and as As in perch and dace. "■"* Vitamin A is not required 

 in the diet of the cockroach, and analyses indicate that this animal does not 

 synthesize it. ^^ Vitamin A has not been found necessary for growth or 

 maintenance of any invertebrate animals, although it is suggested for the 

 snail Helix pomatia. "' Since visual purple occurs in the pigment system of 

 some arthropod and cephalopod eyes (see Chapter 11) the possibihty of a 

 carotene or vitamin A requirement for visual function in these animals should 

 be tested. 



Vitamin D. This is a class of substances, the most important of which are: 

 (1) D2 or calciferol, which is obtained by irradiation of ergosterol, and (2) 

 Da or activated 7-dehydrocholesterol, which occurs in fish liver oil and is syn- 

 thesized in the skin of higher animals under action of sunlight. Vitamin Do 

 is only one-thousandth as active for chickens as is D^, whereas the two forms 

 are nearly equally active for rat and man. Vitamin D increases the absorption 

 of calcium and phosphorus, and its lack results in low bone phosphatase and 

 abnormal bone production, one kind of rickets. It is also needed for proper 

 dentin formation in teeth. Unlike cholesterol, no form of vitamin D has been 

 shown to be essential for any nonvertebrate, but the relation of specific sterols 

 to phosphatase activity in shell deposition in crustaceans and molluscs seems 

 not to have been investigated. 



Vitamin E (a-, /3-, and y -Tocopherols'). The most important form of vita- 

 min E is: 



CH. C 



HOC T: CH. CHs CHa CH3 



I II I III 



CH3-C C C-CH,^CH.-CH.-CH-CCH03-CH-(CH03-CH-CH:, 



\ / \ /\ 



C O CHa 



I 



CHa 



Vitamin E, usually supplied as a-tocopherol, is necessary for normal develop- 

 ment of vertebrates. Deficiency results in degeneration of germinal epithelium 

 in the male and resorption of embryos from female mammals. Local hemor- 

 rhages, blood vessel impairment, brain and liver lesions, and particularly lesions 

 of the testis have been observed in deficient chickens, ' tadpoles, "'^ and fish 

 (guppies-'O- It is likely, therefore, that vitamin E is essential for all classes 

 of vertebrates. It is required for the proper use of vitamin A, probably because 

 of its anti-oxidant properties. Among invertebrates, vitamin E is probably not 

 essential, but in the moth Ephestia a-tocopherol protects linoleic acid from 

 oxidation, although other antioxidants, for example, ascorbic acid, can do as 

 well. 



Vitamin K (Methyl Phytyl Naphthoquinone). Vitamin K is an antihe- 

 morrhagic factor essential for prothrombin formation. Its needs has been 

 demonstrated in several mammals and birds, and it is obtained as Ki from 

 green leaves and as Kj from putrefying fish meal. Supplements of vitamin K 



