.MODIFICATION OF THE GERM-CELLS IN MAMMALS 221 



to fully estimate the actual significance of the differences between 

 the experimental offspring and the control groups used. 



Fortunately, however, the data from the 1916 season is avail- 

 able (Pearl, '16 b) for comparison with the 1915 results. The 

 alcohol treatments were continued throughout the time so that 

 the 1916 chicks are derived from more highly alcoholized parents. 

 Should the alcohol continue to improve the race by ''completely 

 putting out of commission all of the weaker germ cells," the 1916 

 results should in all respects show a further improvement in the 

 qualities that had been previously benefited. 



The percentage of infertile eggs given in the 1915 table may 

 be reversed to per cent of zygotes formed and compared with 

 this column in the 1916 table. The percentage of zygotes formed 

 in the several combinations of alcoholic mating should be less 

 than in 1915, and they are. When both parents were alcoholic 

 in 1915, 40.8 per cent of the eggs formed zygotes, while in 1916 

 only 21.95 per cent produced zygotes; sire only alcoholic, 74.8 

 per cent zygotes in 1915 and only 53.52 per cent in 1916. This 

 is in line with the lowered fertility and increased number of 

 mating failures from the alcoholic guinea-pig records. The more 

 decidedly alcoholic the guinea-pigs become, the smaller the litter 

 size from double alcoholic and sire only alcoholic matings, and 

 the greater the number of failures to conceive. 



With the guinea-pigs, however, this is not alone due to a 

 destruction of weak germ cells by the treatment, but is cer- 

 tainly in part due to an increased very early prenatal mortality 

 for which much evidence is given in the body of the present 

 paper. The smaller number of zygotes formed by the treated 

 fowls is probably also due in some cases to death in very early 

 stages, as blastulae or gastrulae, before the egg is laid ; or in the 

 hen's eggs these weakened zygotes may not be able to with- 

 stand the developmental interruption following the laying of 

 the egg. Embryos dying during such stages could not be iden- 

 tified except by a most minute study. 



It seems to us in keeping with what is known of biological 

 reactions in general and the guinea-pig histories in particular to 

 take the following position. The alcohol treatment acts on the 



