48 R. T. YOUNG 



this are seen in lines la, 6/1 and 6/6 (fig. la), and III, 5/28-6/1 

 (fig. III). 



While endomixis is usually followed by restoration of the 

 division rate, this is not invariably the case, line Ha, 6/15-6/17 

 (fig. Ha). Exceptions to this rule are especially noticeable in 

 those lines which were carried in stale culture media — II, 3/5- 

 3/7, 5/13 (fig. II), Vllb, 2/19, 2/20, 3/24-3/25 (fig. Vllb), etc. 



In order to test the hypothesis that endomixis is a sign of 

 depression I have performed a series of experiments, using the 

 death rate as a criterion of depression. 



When transferred from a culture in which they are abundant 

 to a new hay infusion, I have in several instances been unable 

 to obtain good cultures of Paramaecium and it has only been 

 after one or more trials that I have succeeded in obtaining healthy 

 cultures. I have further found that in isolating single specimens 

 on cover glasses in a few drops of hay infusion a large per cent of 

 such individuals die. The Paramaecia are visibly sensitive to 

 such changes in their environment. When a specimen is placed 

 in a few drops of a new culture fluid, the old culture can usually 

 be recognized in the new by a difference in color. When the 

 animal in swimming about in the old fluid comes in contact with 

 the new it reacts vigorously just as it does when brought in con- 

 tact with a salt solution or other harmful substance, and if it 

 crosses the boundary into the new medium it swims violently 

 about showing in the plainest manner its sensitiveness to the 

 change. The changes moreover to which the animals respond 

 so vigorously are apparently slight, the culture media usually 

 consisting of the same substances (meadow hay and tap water) 

 so that the differences between them consist in age, with conse- 

 quent chemical change, and in the substances given up to the old 

 medium by its inhabitants themselves. 



An exact physico-chemical and biological analysis of a Para- 

 maecium culture would be, to say the least, a very serious prob- 

 lem; and no one has yet, so far as I know, undertaken it, although 

 Peters ('04, '07 a and '07 b), Woodruff ('11 and '12) and Fine 

 ('12) have made a beginning in this very interesting field. 



