D. J. SCOURFIELD OX MBNDELISM AND MI< ROSCOPY. 405 



proportion of three coloured to one albino, might sometimes give 

 rise to pure black mice. It was difficult to see how this could 

 come about, but there was some slight reason for thinking that 

 the black must have been derived in some way from the albino 

 and not from the grey mice. Starting from this point of view, 

 Cuenot imagined that there were two distinct pairs of characters 

 concerned — namely, a pair for the particular colours involved; 

 whether grey or black, and a pair representing, on the one hand, 

 something which allowed the colour, whatever it might be, to 

 show itself, and, on the other, something which prevented the 

 colour appearing, thus producing albinos. The germ-plasm, in 

 fact, was considered not as being represented by the obvious 

 G (grey) and A (albino), as everybody had previously thought, but 

 as requiring for its proper expression the following formula : — 



Dominant characters. Recessive character-.. 



C (colour-promoting factor). A (colour-repressing factor). 



G (grey). B (black). 



It may be thought at first sight that this is merely an example 

 of Mendel's own conception of two or more pairs of characters 

 being associated in the production of an apparently single pair. 

 But really it is quite different, because, not only is the existence 

 of one of the pairs a pure assumption, but, in order that the 

 two pairs of characters may give the result desired, it is necessary 

 to further assume that the characters of one pair have an 

 influence over those of the other pah' — in the case above-men- 

 tioned either promoting or preventing their appearance. This 

 idea of characters belonging to different pairs influencing one 

 another, while the members of each pair are being segregated 

 and inherited strictly according to Mendel's law, is one of 

 exceptional importance, and, judging by recent investigations, 

 seems destined to come more and more into prominence in 

 questions of heredity. It can only be added here that, by the 

 help of the above formula (amplified so as to include the colour 

 yellow), Cuenot was able to explain in simple Mendelian fashion 

 the apparently contradictory results already obtained, and even 

 to forecast the outcome of new kinds of ruatings never previously 

 undertaken. He also found that the inheritance of the coat- 

 pattern of mice could be explained satisfactorily by the same 

 method. Other workers — notably Hurst, with rabbits — have 



