324 OSCAR RIDDLE. 



ism of melanogenesis." This author does not in any way con- 

 sider the bearing of his findings on Mendelian descriptions of the 

 mechanism of the origin of melanin color characters (neither on any 

 aspect of inheritance). Nor as previously stated has any- 

 one, at any time, inquired as to whether the facts obtained in the 

 former sphere are compatible with the assumptions made in the 

 latter. Bertrand's studies had other and quite different objects ; 

 these were : First, to learn the degree of specificity of the enzyme 

 tyrosinase ; the conclusion here being (p. 387) " that the results 

 speak once more against the principle of very absolute specificity 

 which one nowadays often hears applied to enzyme actions." It 

 will be very well for us to bear in mind this result, since, as we 

 shall see, Mendelian description demands a still higer degree of 

 enzyme specificity than the philosophy of biochemists has yet 

 dreamed of. A second object of his work seems to have been 

 to consider the possibility of identifying certain of these tyrosin 

 bodies by the color reactions they give upon oxidation with 

 tyrosinase. A third purpose of the study was concerned with 

 the causes of the rather wide variations in the elementary com- 

 position of different melanins ; he believes that the results give 

 some reason for believing that the simplest melanins arise from 

 the oxidation of tyrosin itself, while the more complex ones 

 those containing sulphur or iron are formed by the oxidation 

 of less complete products of protein hydrolysis namely, tyrosin- 

 containing di- or polypeptids. 1 A fourth and final phase of Bert- 

 rand's investigation touched upon a hitherto unrecognized, but 

 seemingly possible, mode of union between tyrosin and other 

 amino acids. 



It will now be well to briefly sketch a few facts obtained from 

 the study of abnormal tyrosin metabolism, and from pathological 

 pigmentations (melanin) of the human body, as supplementary 

 to the account of melanogenesis which is given above. These 

 facts will also serve to illustrate the dependence of tyrosin oxida- 

 tions upon somatic conditions which may be of such a temporary, 

 intermittent, quantitative, or reversible character as to preclude 



1 In the formation of melanins, condensations as well as oxidations occur, but the 

 former process need not concern us in treating the present theme. 



