MODIFICATION OF THE GERM-CELLS IN MAMMALS 123 



their breeding ability by one normal mating, certain of this lot 

 were taken for alcohol treatment, and these animals were bred 

 both separately and with the original lot.' Yet the records of 

 the alcoholic and normal individuals were again different 



Finally, in October, 1915, when the experiment was five years 

 old, we obtained four new stocks of guinea-pigs from different 

 dealers and introduced them into the experiments in various 

 ways along with our now pedigreed lines from the old stock. 

 The records of these new animals as well as our old lines known 

 for three or more generaitions regarding inbreeding and other 

 conditions are to be considered in the present paper. These 

 experiments bring out additional facts in the study, and we 

 believe they supply an unquestionable control on the previous 

 results. In other words, this may be taken as a new study con- 

 sidering the conditions of 1,170 guinea-pigs born from various 

 alcoholic lines as well as from normal control animals. About 

 600 of the animals are born of alcoholic lines with no inbreed- 

 ing in any case back through their great-grandparents. About 

 300 of them are from alcoholic lines and at the same time some- 

 what inbred; these are for all considerations treated separately 

 from the straight alcoholic lines. The control animals with 

 which the alcoholics are compared are of the same blood lines 

 as the alcoholics and are also not inbred. 



2. QUALITY OF THE EXPERIMENTED AND CONTROL ANIMALS 



a. Selection of animals 



As briefly mentioned above, the control and the first treated 

 individuals are derived from exactly the same original stock. 

 During the progress of the experiment other animals have been 

 subjected to the treatment, and these in many cases are of 

 known pedigree for several generations in our colony. In all 

 cases only vigorous animals are used for the treatment and they 

 are invariably tested by being mated at least once before the 

 treatment is commenced. This precaution is undoubtedly of 

 much importance, equally as important as knowing the blood 

 lines, in selecting normal breeders. These test matings are 



