An Introduction to a Biology 



very simple. I wrote the catalogue-name of each mouse 

 on a counter, then I put the counters representing female 

 mice into one hat and those representing males into another : 

 all that remained to be done was to draw out at random 

 a counter from the " female " hat and similarly one from 

 the " male " hat, and to mate the actual mice represented 

 by these counters. As I have said, this method enables one 

 to test the Law of Ancestral Inheritance and Mendel's Law. 

 As far as the first is concerned, it is the most perfect con- 

 ceivable ; but for the second it is clumsy and involves un- 

 necessary labour, because what is aimed at in a Mendelian 

 experiment is the discovery of the properties of character- 

 units, as far as they can be discovered by determining the 

 specific results of their union with similar and dissimilar 

 character-units. Now some particular combination of char- 

 acters may turn up very seldom by the method of random 

 union ; and if one wishes to discover the result of such a 

 combination one has to wait until the drawings from the 

 hat give it. One is in the position of an observer, and if 

 one wishes to attain the knowledge of the result of such a 

 combination quickly and in large numbers, the random 

 mating and the counters must be discarded and one must 

 deal experimeiUally with the material, isolating the indivi- 

 duals the properties of whose character-units one washes to 

 determine. 



I had planned at the begimiing of last year (1905) to 

 do the same experiment with peas by mating at random 

 peas with green round seeds (Eclipse) with peas with yellow 

 wrinkled seeds (British Queen), and with each other ; and 

 had already sown the seed, when it occurred to me that 

 I need not have done so. We know^ the result of crossing 

 a yellow wrinkled \\ith a green round pea, and of their mating 

 itUer se : so that all that is necessary is to start with a 

 hat containing equal numbers of yellow and green counters 

 representing pistil parents, and a hat with similar contents 



1 Hurst, :0l 

 N 193 



