REQUIREMENTS OF ANIMALS 577 



for maximum life span,^'*^"^''® for satisfactory tooth structure, ^''^ for the 

 maintenance of an optimum plasma vitamin A level, ^^° for the provision of 

 adequate liver stores,^'*'' and the amount needed to produce the optimum 

 vitamin A content in the retina.*^" The vaginal smear method has been 

 employed in rats^^^'^'*^ since the discovery by Evans and Bishop^^'' of the 

 relationship of the vaginal epithelium to vitamin A intake. Mason and 

 Ellison^'' described the method in detail. Tooth color is a useful crite- 

 PJQj^ 946,952 g^j-^(j ^jjg curative action of the product on xerophthalmia offers 

 another approach to the subject. ^^^'^^^'^^^ Lewis et al.^^° used the amount 

 of vitamin A required to prevent deficiency symptoms (xerophthalmia, loss 

 of weight) as a criterion. 



The growth method as described by Coward^ has been widely employed 

 as a bioassay method for the determination of vitamin A. With certain 

 modifications, it has been accepted as the official method for bioassay by 

 the U. S. Pharmacopeia Convention. ^^^ Guerrant^^^ and Bliss and Gy- 

 5j,gy956 described (1951) the growth method and other assay procedures in 

 more detail. While the growth method is extremely accurate when the 

 sensitive and linear portion of the log-dose-growth response curve is stud- 

 ied, the determination of the requirement for optimum growth makes use 

 of the extreme portions of the curve, where there is great likelihood of error, 

 and the results may be quite inaccurate. According to Hegsted,^"^ the 

 errors in this measurement (statistical dose-response) are such as to lead to 

 low estimates for requirements. 



In the case of chickens, hatchability of eggs and survival of the chicks 



9" H. C. Sherman, H. L. Campbell, M. Udiljak, and H. Yarmolinsky, Proc. Nat- 

 Acad. Sci., U.S., 31, 107-109 (1945). 



9" H. C. Sherman and H. Y. Trupp, Proc. Nat. Acad. Sci., U.S., 35, 90-92 (1949). 



9« H. C. Sherman and H. Y. Trupp, /. Nutrition, 37, 467-474 (1949). 



9« H. E. Paul and M. F. Paul, /. Nutrition, 31, 67-78 (1946). 



9" K. Guggenheim and W. Koch, Biochem. J., 38, 256-260 (1944). 



9« H. Goss and H. R. Guilbert, /. Nutrition, 18, 169-179 (1939). 



9« H. R. GuUbert, C. E. HoweU, and G. H. Hart, /. Nutrition, 19, 91-103 (1940). 



«o H. M. Evans and K. S. Bishop, Anat. Record, 23, 17-18 (1922). 



«i K. E. Mason and E. T. ElUson, J. Nutrition, 10, 1-11 (1935). 



9" J. T. Irving and M. B. Richards, Nature, lU, 908-909 (1939). 



963 C. A. Baumann, B. I\I. Riising, and H. Steenbock, Z. Vitaminforsch., 3, 81-89 

 (1934). 



9" Anonymous, U. S. Pharmacopeia, XIV, 1950, pp. 787-792. 



956 N. B. Guerrant, General Aspects of Small Animal Experimentation, in P. G5'6rgy, 

 Vitamin Methods, Vol. 2, Academic Press, New York, 1951, pp. 1-40. 



966 C. I. Bliss and P. Gj-orgy, The Animal Vitamin Assays, in P. Gyorgy, Vitatnin 

 Methods, Vol. 2, Academic Press, New York, 1951, pp. 41-275. 



9" D. U. Hegsted, J. Nutrition, 35, 399-409 (1948). 



