220 CHARLES R. STOCKARD AND GEORGE N. PAPANICOLAOU 



favor of the possibility, that although a sufficiently large dose 

 may have been used, yet it did not act solely to eliminate germ 

 cells as such, but also caused the production of many zygotes 

 which died during early developmental stages. 



The amount of dosage is very important. Treating female 

 guinea-pigs with considerable doses of alcohol fumes only shortly 

 before and during their pregnancies certainly does not injure 

 the offspring to any noticeable degree. While the same dose 

 of treatment, if administered for a number of months or years, 

 will render these mothers almost incapable of producing vigorous 

 young, even when mated with normal males. 



Pearl ('17, p. 281) finds regarding his 1915 results which were 

 obtained after the treatments had been running for only a few 

 months that considering the number of animals in the experi- 

 mental series the individual differences are not in every case 

 sufficiently large to be significant in comparison with their prob- 

 able errors. The control in this case was also not what Pearl 

 had, wished. He had originally chosen a carefully pedigreed 

 control, taking as the one control male a half-brother of the three 

 experimental males and using control females that were sisters 

 of the treated hens as recorded in table 5, p. 158 ('17). The 

 only control male, No. 666, proved to be practically sterile and 

 useless. This necessitated the use in paper No. Ill of an ordi- 

 nary random sample control instead of the refined control 

 originally planned in Part I of the series of papers, and nulli- 

 fied the statement in the summary of Part I, p. 162, that "Full 

 brothers and sisters of treated are used as control." 



For certain qualities, such as the fertility and hatching records 

 of the eggs, the control was not in all cases the same cross as the 

 experiment, which was invariably between Barred Plymouth Rock 

 hens and Black Hamburg cocks. The hatching weight and rate 

 of growth of the experimental chicks on account of want of con- 

 trol data from the 1915 season were compared with chicks from 

 a similar cross hatched and reared in 1913. Different keepers 

 were in charge of rearing the chicks during the two different 

 seasons. These unfortunate conditions, all of which are pointed 

 out with conscientious fullness by Pearl, make it rather difficult 



