XI. REQUIREMENTS 383 



higher reciuirement, iianiely 2 mg. per (lay.'-"- -' Kuether d al.-- ol)taiiied a 

 value of 3 mg. for 300-s- animals, ^'alues of 2.4 mg.-^ and 2.5 mg.^'* have 

 also been reported. It would thus appear that the minimum requirement 

 as judged by the tooth method is 2 to 3 mg. per day, which is actually four 

 to six times as great as that for the prevention of macroscopic symptoms 

 in other organs and tissues. 



c. TwenUj-Four-Hoiir Urinary Excretion of the Vitamin 



This method has been found to be an unreliable indicator of the ascorbic 

 acid status-^ in man and would not be usable in the guinea pig, since it does 

 not excrete ascorbic acid except with dosage levels which are higher than 

 the requirements. By the use of test or saturation doses-^ in man, the 

 results are somewhat better, the amount excreted depending on the plasma 

 concentration which in turn depends on the degree of depletion of 

 the tissues. 



d. Methods Involving Measurements in Blood 



(1) Fasting Plasma Concentration. This method has been found to give a 

 more accurate index of the ascorbic acid status than the 24-hour urinary 

 excretion test and is simpler than the test dose procedure.'-^- -* In the guinea 

 pig Giroud et al.^ reported that doses of more than 50 mg. daily were neces- 

 sary to maintain growing animals in health. With this dosage the amount 

 found in the tissues is about the same as that found in animals which syn- 

 thesize the \'itamin. Most workers in this field, however, consider this level 

 to be higher than is necessary. Penney and Zilva-^ found that an intake of 

 25 mg. daily was necessary to maintain saturation of the tissues in 300-g. 

 guinea pigs. There appeared to be no definite correlation between the tissue 

 content and the onset of scorbutic lesions, provided that the intake ex- 

 ceeded 1 mg. per day. The survival time of initially saturated animals on 

 a scorbutigenic diet was no longer than that of animals whose initial tissue 

 concentration was about half the saturation value. They interpreted this 

 as suggesting that at least the fraction of ascorbic acid lost from the tissues 



" L. J. Harris and S. N. Ray, Biochem. J. 27, 2016 (1933). 



2> K. M. Key and B. G. E. Morgan, Biochem. J. 27, 1030 (1933). 



" C. A. Kuether, I. R. Telford, and J. H. Roe, /. Nutrition 28, 347 (1944). 



" H. C. Hou, Chinese J. Physiol. 10, 213 (1936). 



" M. B. Cohen, Am. J. Diseases Children 60, 636 (1940). 



" E. P. Ralli, G. J. Friedman, and S. Sherry, J. Clin. Invest. 18, 705 (1939). 



" E. P. Ralli, G. J. Friedman, and M. Kaslow, Proc. Soc. Exptl. Biol. .Med. 36, 52 



(1937). 

 " L. D. Greenberg, J. F. Rinehart, and N. M. Phatak, Proc. Soc. Exptl. Biol. Med. 



35, 135 (1936). 

 28 A. F. Abt and C. J. Farmer, J. Am. Med. A.ssoc. Ill, 1555 (1938). 

 " J. R. Penney and S. S. Zilva, Biochem. J. 40, 695 (1946). 



