3 i 6 Vierte allgemeine Sitzung. 



let us not neglect to see, are incapable alike of further subdivi- 

 s i o n into factors, and of complete segregation in 

 gametogenesis. Chromogen, for example, being quite incapable 

 of any such segregation for the simple reason that it is found 

 wherever protoplasm is found. 



Durham nowhere in the presentation of her results men- 

 tions any color other than the final one as having appeared in the 

 oxidation of tyrosin to black. A thing that must occur when 

 t y r o s i n is oxidized by tyrosinase. Such a series of 

 colors is known to be so produced no matter from how widely 

 separated the source of the enzyme; whether these come from a 

 mushroom or a squid; from wheat bran or the melanotic tumor 

 of a horse. Such an important general characteric of tyrosinase, 

 should have been neither unknown nor disregarded by one in search 

 of specific tyrosinases. Perhaps if the final and complete paper 

 had been published this point would have been cleared up. 



It must be said further that the color reactions with which 

 we are dealing in these experiments with the birds', or mammals 

 skins are not simple and quite well understood. Such extracts as 

 we get with the methods used contain a world of things besides oxi- 

 dases ; and I find myself at present unwilling to make very positive 

 Statements even about the colored substance with which we here 

 have to do. It certainly is not all melanin, at least not all melanin 

 of the usual kinds, as Durham seems to have had no doubt ; 

 sometimes on the contrary, for example, quite all of the black 

 precipitate or Suspension has readily dissolved in acetic, and the 

 mineral acids. The füll and complete consideration of the me- 

 thods, and a tabulated account of my experiments with the 

 extracts of bird's skins must be given elsewhere; while the nature 

 of the substances produced in the putrefying Juices, and the 

 alleged röle of the ferrous sulphate, are still under investigation 

 and cannot now be fully or properly described. 



What we do here emphasize, and what we believe we have 

 definitely proved, is that D u r h a m 's substantiation of the 

 presence and absence hypothesis does not hold; and indeed that 

 specific color — in birds' skins at least — does not seem to be 

 associated with specific color-producing enzymes. 



We may add that our findings seem to be supported too 

 by those of Gortner (1910) who has very recently made 

 some opportune and necessary observations on the evidence 

 obtained by Durham for the specificity of tyrosinases in the 

 skins of vertebrates. Gortner gives but a paragraph to this 

 subject, but the following lines are significant. He states "the 

 author has made several attempts to confirm her results but 

 has as yet obtained no trace of coloration induced by an oxydase". 



Our conclusion is then that the basic postulates of C u e n o t 's 

 presence and absence' theory have failed of the necessary chemical 



