98 VITAMINS A AND CAROTENES 



female animals; therefore equal numbers of males and females are used for 

 the experiment. The age of the experimental animals should be 20 to 22 

 days, and their weight should not exceed 30 to 40 g.^"^ 



Vitamin A-deficiency diets are given by Bacharach and his collabo- 

 rators^i" and others.^"- ^^^ Jiirgens^"^ recommends: 



100.0% 



" The vitamin A was destroyed by heating up to 90° and simultaneous passing air through for 8 hours. 

 Sodium chloride, 5.0%; calcium lactate, 35.0%; calcium phosphate, 15.0%; ferrous citrate, 3.21%; po- 

 tassium iodide, 0.09%; copper sulfate, 0.03%; magnesium sulfate, 5.5%,; potassium phosphate, 26.53%; so- 

 dium phosphate, 9.6%; zinc carbonate, 0.02%; manganese sulfate, 0.02%; sodium fluoride, 0.003%. 



In recent investigations attention was drawn to the synergism existing 

 between vitamin A and tocopherol. Thus, through the presence of tocoph- 

 erol a favorable influence is exerted on the storage of vitamin A and caro- 

 tene.^^^""^ With the storage test the saving of vitamin A has to be taken 

 into consideration, conditional to this special test (see below). 



For biological evaluation the growth test is preferred. Generally, animals 

 fed on a vitamin A-free diet are fit for the test after 6 to 7 weeks, as evi- 

 denced by the cessation of growth and the appearance of the first symptoms 

 of xerophthalmia. In all experiments the parallel testing of a vitamin A 

 standard preparation is essential. During the testing period the vitamin A 

 standard as well as the sample to be examined are given daily, and the 

 growth of the animals — ^that is, their gain in weight — ^is observed for at 

 least 4 weeks. Only animals of the same sex are comparable. Gridgeman^°^ 

 has worked out a method for the evaluation (see also Irwin^^^). The details 

 may be found in the original literature.^"^ 



Lately, the storage test of Guggenheim and Koch'^^ is being recommended 

 as more valid than the growth test. This test requires only one-third to one- 

 fourth the time needed for the growth test. Rats 18 to 22 days old and 



^"' R. Jurgens, Arzneimittel-Forsch. 1, 119 (1951). 



"" A. L. Bacharach, E. M. Cruickshank, K. M. Henry, S. K. Kon, J. A. Lovern, 



T. Moore, and R. A. Morton, Brit. Med. J. 1942, II, 691. 

 "1 C. A. Cabell and N. R. Ellis, Proc. Soc. Exptl. Biol. Med. 65, 117 (1947). 

 ^^^ L. Randoin and J. Causeret, Biill. soc. sci. hyg. aliment. 35, 14 (1947). 

 "» K. C. D. Hickmann, Ann. Rev. Biochem. 12, 356 (1943). 



1" K. C. D. Hickmann, M. W. Kaley, and P. L. Harris, J. Biol. Chem. 152, 313 (1944). 

 '" T. Moore, Biochem. J. 34, 1321 (1940). 

 "« J. O. Irwin, J. Hyg. 43, 291 (1944). 

 1" K. Guggenheim and W. Koch, Biochem. J. 38, 256 (1944). 



