EVIDENCE OF GERM CELL SELECTION 387 



Mendelian characters were being investigated. Since some of 

 these characters were not represented in Pearl's material, and 

 the writer was at the time casting about for a method to test 

 for germ-cell selection, it seemed worth while to continue breed- 

 ing from the same birds with former conditions maintained 

 except for the introduction of alcohol treatment. The work 

 was planned in no sense as a repetition of Pearl's experiments, 

 but rather as an attempt to extend his methods to a few characters 

 not known to be directly dependent upon inherent vitality. 

 The writer takes this opportunity of acknowledging his in- 

 debtedness to the valuable and suggestive paper mentioned 

 above. 



The first experiment, 1, was made in the spring of 1917 with 

 results that seemed to point to a selective action of the alcohol 

 vapor. The matter is one of such importance, however, that 

 a repetition of the work seemed desirable before publication 

 of the data. Consequently three further experiments, 2, 3, 

 and 4, were carried out in the spring of 1918. As will appear 

 below^, the results obtained in the latter work proved to be 

 essentially consistent with the findings in the first experiment, 

 which fact seems to justify their publication. 



GENERAL NATURE OF THE EXPERIMENTS 



In each experiment a cross was made between normal, pure- 

 bred stock on the one hand and hybrid, heterozygous birds on 

 the other. The hybrid individuals were subjected for certain 

 periods to two daily treatments with alcohol vapor, during which 

 time as far as possible all eggs laid were incubated (table 2). 

 Since the original purpose of the work was to test the possi- 

 bility of selecting germ cells rather than of modifying them 

 through influences brought to bear on the soma, each experi- 

 ment is brief and intensive. 



A control was obtained in each case by saving the eggs from 

 the same flock, kept under as nearly identical conditions as 

 possible, during a period before or after the alcohol experiment. 

 All eggs that did not hatch were opened and the character of 



