74 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 6 



developed a spectrophotometry method, and also a sedimen- 

 tation method by which the volume of the precipitate is 

 measured in graduated centrifuge tubes, but neither seemed 

 to give wholly consistent and reliable results and the methods 

 were not tried out. 



A third method was proposed by Bach ('08 a ), in which the 

 colored solution was titrated by N/500 potassium perman- 

 ganate until the color disappeared. This method was tried 

 out early in this work, but I was unable to titrate to a definite 

 end point. Perhaps had I had the experience in matching 

 colors which was developed later in connection with the 

 colorimetric method, I might have secured more uniform 

 results such as Bach was able to obtain. As with many meth- 

 ods, the personal equation plays a large part in the accuracy 

 obtainable. 



A fourth method was that used by Chodat and Staub ('07) 

 and by Staub ( '08), in which a series of standards were made 

 up by means of Bismarck brown and corallin to fit the usual 

 degrees of color change and were compared with the unknown. 

 This method gave them comparative results, but was hardly 

 suited to my purpose. 



The last set of methods was employed in the gas exchange 

 work, usually limited to a study of the amount of gas absorbed. 

 The method of Bunzel ( '12, '14) was tried with the commer- 

 cial form of his apparatus, but was wholly unsuccessful. The 

 apparatus is too small to admit enough of the tyrosin solu- 

 tion to absorb a measurable amount of oxygen. The Mc- 

 Nair modification of the Van Slyke apparatus for the deter- 

 mination of amino-nitrogen is much more useful in every way 



and gives more consistent results. The procedure was modi- 

 fied slightly for rapidity of determination, as will be described 

 later. 



Methods used 



— In this study an at 



tempt was made to determine the amounts of the various 

 reacting portions of the tyrosin molecule, thus hoping to se- 

 cure a suggestion as to the actual chemical changes taking 

 place in the formation of " melanin' ' and other pigments, due 

 to the action of tyrosinase on tyrosin. A glance at the struc- 



