MODIFICATION OF THE GERM-CELLS IN MAMMALS 155 



the females and determining the exact time of the ' heat periods' 

 (Stockard and Papanicolaou, '17). This has enabled us to pair 

 the animals at the most favorable periods and thus to obtain far 

 better and more exact mating records than was possible on the 

 basis of the previous conceptions of the guinea-pig's sexual be- 

 havior. Secondly, the housing, care, and feeding of the animals 

 are decidedly better during the last three years than during 

 previous times, and on this account the mortality in all lines 

 has been reduced, but as might be expected, the weaker alcoholic 

 lines have profited more by this improved condition than have 

 the control animals. For example, the mortality record of the 

 control has been lowered only a little more than 3 per cent, while 

 in the alcoholic lines it has been lowered a much as 18 per cent. 

 This improvement in the alcoholic lines is also partly due to the 

 existence of more late-generation animals with many normal 

 ancestors. Thus, although the lowered mortality record of the 

 alcoholic may not be entirely due to the better living condi- 

 tions, yet it serves as a striking illustration of the difference in 

 response to the change on the part of the control animals and 

 the alcoholics. The previous somewhat unfavorable state did 

 not greatly impair the powers of existence of the control ani- 

 mals, but it did evidently eliminate some of the weaker alco- 

 holic individuals that might have survived under more ideal 

 arrangements. 



It must be recognized, in the third place, that for the alcoholic 

 inbred animals the degree of inbreeding among the later gen- 

 erations here included is less intense than was the case with 

 earlier generations in the former reports. And for this reason 

 the previous rather decided differences which were shown be- 

 tween the straight alcoholic group and the alcoholic inbred ani- 

 mals have almost, though not entirely disappeared. 



Lastly, the fourth point of difference to be borne in mind in 

 comparing the earlier and present records is that there are now 

 more late-generation alcoholic descendants with less affected 

 material in their total germ-cell complex than was true of the ani- 

 mals in the former tables, which as a group were composed of 

 generations closer to the direct alcohol treatment. For ex- 



