Chemistry of Coat-Colour in Animals. 



39 



duction of an orange precipitate from tyrosine, as in the case of Miss Durham's 

 red guinea-pigs, must have been of a totally different nature from any hitherto 

 known. It is true that some tyrosine-oxidising ferments commence with a 

 yellow or orange stage, but they finally turn black. Miss Durham also states 

 that she extracted a tyrosinase of a less active nature from adult guinea-pigs, 

 I, however, was entirely unable to obtain any ferment from four months old 

 rabbits. Eiddle* also criticises Miss Durham's work, on the grounds that her 

 extract appeared reddish, which he claims would modify the final colour. In 

 addition to this, an oxygen carrier like oxyhemoglobin, which is no doubt 

 the cause of the reddish colour, would seriously interfere with the results. 

 Finally, Gortnerf says that he has made several attempts to confirm these 

 experiments without success. Moreover he has shown that the addition of 

 1 mgrm. of ferrous sulphate completely inhibits the action of tyrosinase, 

 an observation which I have been able to confirm. It seems possible, therefore, 

 that Miss Durham's results were due to some combination of the iron with a 

 protein molecule, or else to some degenerative change or autolysis accompanied 

 by pigment production, such as that called by Meirowsky^ post-mortem 

 pigment production, which he showed took place even in pieces of boiled skin 

 if they were kept for a few days in the warmth. My own results with 

 material obtained from the skins of young black rabbits by Miss Durham's 

 methods are in full agreement with those of G-ortner. And one must conclude 

 that the results so obtained are not due to the action of a tyrosinase as usually 

 understood, but to some other unexplained cause. 



2. The Peroxidase Present in the Skins of Coloured Rabbits and. Mice. 



It has already been pointed out that, according to the theory of Bach and 

 Chodat, an oxidase is of a dual nature, the two constituents being a peroxide 

 and a peroxidase, the peroxide functioning as an activator to the peroxidase, 

 by supplying it with oxygen from the atmosphere!, which may then be 

 transferred to the chromogen or other oxidisable body. It was therefore thought 

 possible that not only the chromogen but also the peroxide constituent of 

 the tyrosinase had been destroyed during the process of making the extracts 

 from the skins. In order to test this, a very small quantity of hydrogen 

 peroxide, which has been shown to be capable of replacing an organic 

 peroxide of an oxidase system, was added to the extract, in addition to 

 tyrosine, and the tube was then incubated. After 12 hours its appearance 



* Eiddle, 'Biol. Bulletin,' vol. 16, p. 316 (May, 190!)). 

 t Gortner, 'Trans. Chem. Soc.,' vol. 97, p. 110 (1910). 



% Meirowsky, ' Centralbl. fiir allg. Path. u. patholog. Auat.,' vol. 20, p. 301 (1909) ; see 

 also KOnigstein, ' Wiener Klin. Wochenschiift,' No. 17, p. 616 (1910). 



