MELANIN COLOR FORMATION. 323 



into melanin pigment. Thus the whole series of compounds in the 

 table given below (and many others besides) can be oxidized to 

 colored compounds. On the other hand, phenylalanine, phenyl- 

 methylamine, phenylominoacetic, phenylpropionic and phenyl- 

 acetic acids, alanin, glycocoll, etc., give no coloration whatever. 



t 



The size, complexity, and nature of the lateral chain has only a 

 subordinate influence ; if it is not very strongly acid or basic it will 

 not interfere with the oxidation. Thus for example, ethyltyrosin, 

 chloracetyltyrosin, and glycyltyrosin were oxidized with ease. 

 The nature of these side chains does, however, considerably modify 

 the colors produced by the oxidation. Neither of the three last 

 named bodies (tyrosin compounds) give a final black color ; they 

 begin with orange or yellow and end with red or mahogany 

 (chocolate ?). 



In order to further appreciate something of the variety of color 

 which may arise from a single cliromogen, and to get an introduc- 

 tory idea of the number and variety of chromogens to be found 

 in the animal body, careful reference to Table I. should be made. 

 And here it is of the higlicst importance to see that a single chro- 

 mogcn acted upon by a single enzyme (so far as all chemical ex- 

 perience has detected) produces several colors depending upon the 

 degree of oxidation involved. 



In regard to the rate at which these colors appeared the 

 author's statement may be cited that in a 20 per cent, tyrosinase 

 (80 per cent, strong tyrosin) solution, tyrosin developed a rose 

 color in ten minutes and its black color in four to five hours. 



TABLE I. (From Bertrand, '08.) 



Name of Body. Colors Produced by Oxidation. 



Tyrosin red grenadine, then inky black, 



p-oxyphenylethylamine red grenadine, then black olivaceous, 



p-oxyphenylmethylamine orange yellow, orange red, maroon, 



p-oxyphenylamine orange, mahogany red, then brown, 



p-oxyphenylpropionic acid orange yellow, grenadine red, brown, 



p-oxyphenylacetic yellow, orange yellow, then brown, 



p-oxybenzoic " (weak) rose, orange, then yellow, 



p-cresol yellow, orange, then red. 



Phenol yellow, orange, red, then brown. 



These are, from our present point of view, the more notable 

 results of Bertrand's investigations of what he calls " the mechan- 



