222 CHARLES R. STOCKARD AND GEORGE N. PAPANICOLAOU 



germ cell populations of both fowls and guinea-pigs in such a 

 manner that the weakest or least resistant ova and spermatozoa 

 die from the effects of the treatment as germ cells without taking 

 part in zygote formation. The somewhat more resistant ova 

 and spermatozoa are greatly injured though still capable of 

 forming zygotes. The zygotes, however, are so defective as to 

 be capable of only a short period of development and die during 

 stages too early to be definitely detected by gross examinations of 

 either the fowl's egg or the mammalian mother. Still other em- 

 bryos are capable of development to later stages and are actu- 

 ally found dead, not only as the youngest embryos to be identi- 

 fied, but from these early stages there occurs a continuous series 

 of prenatal deaths up to the full-term still-births. Immedi- 

 ately after birth the postnatal mortality is greatest and gradu- 

 ally decreases until these specimens capable of reaching maturity 

 may often enjoy a comparatively long life. 



At the present stage of the two experiments it would seem as 

 though this elimination of defective germ cells and very early 

 embryos was much more intense in the fowls than in the guinea- 

 pigs as a group; so that the late prenatal and postnatal mor- 

 tality among the fowl progeny was low and those specimens 

 that hatched were the hardy survivors from this early vigorous 

 process of germ cell and individual selection. The records from 

 the double alcoholic and male treated lines among the guinea- 

 pigs forms a second step. The size of the litters and failures 

 to conceive in these lines indicates a rather high degree of in- 

 fertility or germ cell debility as well as early prenatal deaths, 

 though this is not so extreme as among the fowls, and the late 

 prenatal and postnatal mortality is higher. 



Finally the female treated guinea-pig lines produce large lit- 

 ters and have few infertile matings, indicating a low germ cell 

 and early prenatal mortality, and here the late prenatal and 

 postnatal mortality is highest, not entirely on account of the 

 action of the treatment on the developing individual in utero, 

 since the same condition is found among other female gene- 

 rations than the one directly treated. 



This presentation of the situation is somewhat similar to that 



