350 PROCEEDINGS OF THE OHIO ACADEMY OF SCIENCE. 



with the full potentiality of youth. The logical conclusion is- 

 that natural death is a function of the metazoan but not of the 

 protozoan, — that the protozoan is as undying as the germ cells 

 of the metazoan. The conclusion is unassailable if the premises 

 are correct ; but the latter have been vigorously questioned by 

 Calkins in a series of papers beginning in 1902. Calkins sees in 

 the protozoan a life cycle divided, like that of the metazoa, into 

 youth, maturity, and senescence, and terminating in natural 

 death. Here it should be emphasized that Calkins finds the 

 equivalent of the metazoan individual not in the individual pro- 

 tozoan cell, but in the entire multitude of cells produced by fis- 

 sion between two conjugation periods. By a very carefully 

 executed iseries of experiments, in which paramecia were cul- 

 tivated in sterile hay infusion and isolated at intervals so fre- 

 quent as to eliminate all possibility of conjugation, the division 

 rate (taken as a measure of general body activity) was shown 

 to fall off rapidly after some two hundred generations. Death 

 would then ensue in the absence of conjugation, unless the pro- 

 toplasm was artificially stimulated by chemical treatment. Fi- 

 nally, after some 742 geenrations extending through twenty-two 

 months, a condition was reached in which such stimulation was 

 unavailing, and the strain died out. Meantime such individuals 

 as had been permitted to conjugate had established new lines 

 comparable with new metazoan individuals. Death and conjuga- 

 tion would seem to be as necessary in the protozoa and as closely 

 related as death and sexual reproduction in the metazoa. 



On May i, 1907, Woodruff started a similar isolation cul- 

 ture of Paramecium, modifying the method of Calkins by the 

 substitution of sterile pond water of varying chemical constitu- 

 tion for the too uniform hay infusion. The results are striking 

 in the extreme. On November 15, 191 5, eight and a half years 

 after the beginning of the experiment, the culture was in good 

 condition and had reached the 5375th. generation, — and this 

 without conjugation, without periods of depression, and with- 

 out artificial stimulation. 



In the earlier part of the experiment no conjugation was 

 observed in the mass cultures carried along with the isolation 



