Physiological Ontogeny. A. Chicken Embryos. Ix . ~ Iodine Reaction for the Quantitative Determination

The importance of the sulphydryl compound, glutathione, as one of the thermostable components of the oxidation-reduction system of living cells has been established by Sir F. G. Hopkins ( i) and his assoda t e s in the Biochemical Labora tory , Cambridge, and recent ly a me thod for the quant i ta t ive estimation o f S H groups in tissue has been proposed by Tunnicliffe (2). In a s tudy of the chemical and physiological changes with age in chicken embryos, therefore, i t would seem desirable to include an analysis of the tissues for glutathione. I t would be interest ing to know whether the concentrat ion of this impor t an t substance is posit ively correlated with the velocity of such phenomena as growth and catabolism.