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Vierte allgemeine Sitzung. 



and orientation, permit us an Observation concerning the parentage 

 — the essential nature and basis — of the new-born theory. Even 

 a glance at the offspring certifies that its moulding mother is the 

 Theory of Representative Particles as this had ripened and matured 

 from the Pangenesis of 1868 to the Mendelism of 1900. To 

 this, a young and vigorous paternity added the new and specific 

 features in the form of a few well-proved Bio-chemical Facts Con- 

 cerning the Origin of Melanin Color. From the union then of the 

 representative-particle idea with an experience in color chemistry 

 there was generated the presence and absence hypothesis. Precisely 

 what these hypothesis -begetting facts were, we shall brieflystate. 



Cuenot found that certain albino mice produced in his hybri- 

 dization experiments were capable — albino mated with albino 

 ■ — of producing mice with color. This result could be explained 

 upon the assumption that two distinct and separable things are 

 concerned in the production of color, and that one mouse of such 

 a pair carried one, the other mouse the other of these color-forming 

 pre-requisites. In fertilisation these separable color-forming factors 

 would be united, and thus from albino parents a color-producing 

 zygote would be formed 1 ). 



It was known to Cuenot that chemical investigation 

 had already indicated that two very different sorts of chemical 

 bodies are necessary for the production of melanin pigment — the 

 kind of pigment found in the hair and skin of his mice. These 

 two kinds of substance are chromogen and e n z y m e. 

 The chromogens being colorless substances which are elaborated 

 in, and produce (some of) the colors of, organisms. Several of 

 these were known. The enzymes concerned in color formation 

 are oxidizing enzymes of a variety known as tryosinase. It was 

 not known whether there are many, few, or but one kind of tyro- 

 sinase. 



To Cuenot it seemed reasonable to suppose, therefore, 

 that the things which he assumed were separable in the gametes 

 of his mice, and which might be either present or absent there, 

 were none other than just these chromogens and enzymes. In 

 order to explain the several distinct colors of mice — black, 

 yellow, gray, chocolate, etc. — it was, he thought, only necessary 

 further to assume that a specific chromogen, or a specific zymogen 

 presides over the formation of each of such colors, and that such 

 specificity is represented in, and maintained by, a segregable 

 particle in the germ cell. 



This is a slightly inaccurate, because incomplete, account of 

 the basis of Cuenot' s theory ; but it does f urnish a short 

 story and a clear picture of the chemical phases of the questions 

 involved. 



2 ) For a more exact Statement see Cuenot (1903). 



