02 PHYSIOLOGICAL GENETICS 



results were obtained for larvae, pupae, and flies, also different 

 results for different treatments. For example, sometimes living 

 larvae yielded little or no enzyme, which was increased after 

 addition of chloroform or after grinding the tissues with sand. 

 Young flies did ao1 \ ield any enzyme at all. Graubard concludes 

 that the enzyme concentration may be of no importance at all 

 for melanin formation but that the decisive action rests with the 

 internal environment, which controls how much of the enzyme 

 may take part in the reaction. Another fact seems to corrobo- 

 rate this. Extracts prepared under the same conditions may 

 contain tyrosinase in the following diminishing order for the 

 races tested : 



1. In pupae: yellow, wild, black, ebony. 



2. In larvae: yellow, black, wild, ebony. 



Graubard concludes, therefore, "that it is certain that Gold- 

 schmidt's picture of the gene-enzyme end-result relationship is 

 far too simplified." It seems doubtful whether this analysis lends 

 itself to reliable conclusions upon the genie action. 



1. It is not necessarily the enzyme that is supposed to vary in 

 concentration; it might also be the chromogen. 



2. The variable might be neither enzyme nor chromogen but 

 the time of onset or of ending of the oxidation process. 



3. A measurement of the oxidase content of the whole animal 

 may be irrelevant for the happenings in the cells or organs that 

 deposit the pigment. 



4. Methods that do not permit the discovery of any enzyme in 

 the young fly before darkening can hardly be called sufficiently 

 quantitative to permit of conclusions. 



5. The assumed inhibiting action of the internal environment 

 may be identical with the selective distribution of the enzyme 

 to the regions of action. 



In this connection, we must consider the work of Schmalfuss 

 and Werner (1926) who attacked the problem as chemists in 

 model experiments. They used as a chromogen an amino acid 

 ( 1-/3-3, 4-dioxyphenyl-a-amino propionic acid) and as oxidase a 

 ferment from the blood of caterpillars. The blood was soaked 

 into strips of filter paper and dried. Chromogen was added to 

 these strips, and pigment formation occurred; the conditions of 

 pigmentation were then studied. It was first found that melanin 

 formation depends upon the pH. Acids interfere with the action 



