The Effect of Cystine on the Endogenous Metabolism of Molting Hens

Osborne and Mende1, Johns and Finks2, Sure3, Jones and Murphy4, and others, have studied the need of the animal organism for cystine. As a result of their work cystine is generally recognized as being one of the essential amino acids. Jones, Gersdorff and Moeller5 tabulated the cystine content of various proteins. Lewis6–7 has shown “that the addition of cystine in small amounts to the food of dogs maintained on a low protein level diminished the loss of nitrogen from the body and favorably influenced the nitrogen balance.” He considered the effect of cystine to be specific. The writers8 found a marked increase in the endogenous loss of nitrogen of molting birds from the normal level of non-molting birds. They9 likewise found that cystine increased the extent to which casein is utilized by hens, as indicated, by the nitrogen retained by birds fed equal amounts of casein. The fact that . . .