MODIFICATION OF THE GERM-CELLS IN MAMMALS 129 



compartments one foot high by one foot wide by two feet long. 

 Each compartment is sufficient to fully accommodate one .'^emale 

 with her litter of young or three adult animals. In all of the 

 cages some of the compartments are occupied by the alcoholic 

 animals and others by the control so that the cage accommoda- 

 tions for the tw^o classes are identical. The cages are thoroughly 

 cleaned, the floor sprinkled with sawdust and fresh hay put in 

 daily. In addition to the hay, which is eaten with relish, the 

 animals are fed every day with fresh carrots and several times 

 per week oats are given with occasional cabbage or kale. It is 

 also important for their perfect health, though not necessary for 

 their existence, that guinea-pigs be given fresh water every day 

 during the warmer months and several times per week during 

 the winter. This is frequently neglected in keeping these ani- 

 mals since it is commonly thought that they get__ a sufficient 

 amount of water from the green foods. At the present stage of 

 this experiment, along with several other problems now being 

 studied, a stock of over 500 animals is constantly kept on hand. 

 One reliable keeper devotes his entire time to cleaning the cages 

 and feeding. He in no case discriminates in his treatment of 

 different animals and from the cage numbers is unable to know 

 all of the alcoholic line animals or the controls. 



From the beginning of this experiment, in making the matings 

 a male is placed in a compartment with one female during her 

 heat period (Stockard and Papanicolaou, '17) ; in this way there 

 is no opportunity for preferential or choice matings. A male 

 might discriminate in his behavior between an alcoholic and a 

 normal female if in a compartment with the two, as Pearl be- 

 lieves his roosters have done when placed in a pen with both 

 normal and alcoholic hens. After the male has remained in the 

 pen for one month, the female is carefully examined and at this 

 time with some practice the investigator may feel the small 

 embryos in the horns of the uterus. The male is removed and 

 the female remains alone in the compartment. A list of all preg- 

 nant animals, both alcoholic and control, is kept and their com- 

 ■ partments are examined both morning and late afternoon of each 

 day in order to detect an abortion should it occur, since the 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY. VOL. 26, NO. 1 



