July 20, 1917] 



SCIENCE 



71 



may also throw some light on the nature of 

 protoplasm in that it gives information con- 

 cerning the lower limit of metabolism neces- 

 sary for life. 



In a series of experiments made in connec- 

 tion with other work on Didinium described 

 elsewhere, it was found that the cysts live 

 much longer than had been anticipated. On 

 June 11, 1910, several didinia, all derived 

 from the same individual, were put into a 

 100 CO. beaker containing 50 c.c. of solution 

 with numerous paramecia. The beaker was 

 then placed in a damp chamber and left until 

 January 15, 1911. At this time many didinia 

 cysts were found in the beaker, and no active 

 organisms except a few rotifers. It is not 

 known just when these cysts were formed, but, 

 judging from what usually occurs under 

 similar circumstances, they were probably all 

 formed within a week after the didinia had 

 been added to the culture of paramecia, i. e., 

 about the middle of Jime, 1910. 



On May 31, 1911, a 10 c.c. vial was filled 

 with solution from the beaker containing 

 about one half the cysts. The vial was then 

 corked, sealed airtight with paraffin and laid 

 away in a dark drawer. The remaining cysts 

 were added to a portion of a vigorous culture 

 of paramecia, and the rest of this culture was 

 retained as a control. Two days later there 

 were several didinia in the portion seeded 

 with cysts, none in the control, showing that 

 the cysts were still viable. A few cysts were 

 removed from the vial and similarly tested on 

 each of the following dates : October 22, 1912 ; 

 January 23, 1914; December 12, 1914; Jan- 

 uary 7, 1915; March 1, 1915, and March 4, 

 1915. In all of these tests except two, De- 

 cember 12, 1914, and January 7, 1915, active 

 didinia were secured from the cysts. No di- 

 dinia were found in any of the control cul- 

 tures. This proves conclusively that the 

 cysts of Didinium nasutum can live, at least, 

 nearly five years. 



In all of the tests observations were made 

 daily. In the test of October, 1912, active 

 didinia were found on the fifth day after 

 adding paramecia, in those of January, 1914, 

 on the second day, and in those of March, 



1915, on the sixth and tenth days respec- 

 tively. 



In each of these tests, except the first two 

 and the last, four watch glasses containing 

 cultures of paramecia were seeded with the 

 cysts. In the last test, March 4, 1915, all 

 of the remaining cysts were added to two liter 

 jars containing vigorous cultures of para- 

 mecia. In the test of January, 1914, didinia 

 appeared in three of the watch glasses, in 

 those of December, 1914, and January, 1915, 

 in none, although observations were made for 

 more than two weeks; in those of March 1, 

 1915, active didinia appeared in only one of 

 the four watch glasses; but in the last test 

 of the series they appeared in both jars. 

 In one of these jars only a few small speci- 

 mens were found and these soon died out; 

 in the other, however, the didinia appeared 

 to be perfectly normal ; they developed rapidly 

 and produced a vigorous culture which is 

 still in existence, February, 1917. 



It is thus evident that some of the cysts 

 were still viable at the close of our experi- 

 ment, which extended through nearly five 

 years, but it is not clear how much longer 

 they could have remained viable. However, 

 at the close of the experiment the cysts were 

 much shriveled, only partially filled with pro- 

 toplasm, and yellowish in color, whereas in 

 the beginning they were well filled with proto- 

 plasmic granules and grayish in color. To- 

 ward the close of the experiment the propor- 

 tion of failures was also much larger than at 

 the beginning. All this indicates that the 

 cysts would probably not have lived much 

 longer. On the other hand only a very small 

 proportion of the cysts developed in any of 

 the tests, probably not more than two per 

 cent. Consequently, since the cysts became 

 less numerous as the experiment proceeded 

 the large proportion of failures toward the 

 close may have been due to an insvifficient 

 number of cysts rather than to their age. 



We have thus demonstrated conclusively 

 that didinia in the encysted state can live 

 nearly five years in a solution from which 

 they probably get nothing in the nature of 

 food. If the cysts are dried they probably 



