2O4 GARY N. CALKINS. 



which Maupas experienced in getting fertile endogamous ex- 

 conjugants can be explained upon the same grounds. In one 

 instance I treated an endogamous ex-conjugant with beef extract. 

 The effect was most remarkable for it not only continued to live, 

 but it is still living in tlie jjOt/t generation. When it is remem- 

 bered that the usual life-cycle of Parauiccciuin in culture is from 

 150 to 170 generations, this result is extremely interesting. 



The facts of conjugation thus seem to fit in with the inter- 

 pretation of the other results, to indicate that the protoplasm of 

 this one-celled organism, like a galvanic battery, starts with a 

 high potential of activity, which gradually fails with use, but which 

 may be restored again and again by the proper chemical means. 

 It is to such an assumption that we may turn for an explanation 

 of the periods of depression that have occurred from time to 

 time. The June period, at the 62Oth generation, appears to 

 have been different from the earlier ones, for at this time, neither 

 beef-extract, nor any of the salts that had been successful 

 before, would restore the lagging energies. It was only the use 

 of something entirely different from everything previously em- 

 ployed that finally saved the culture. It may have been the 

 lecithine and allied substances in the brain extract, and it may 

 have been the nucleinic acid in the pancreas extract ; whatever 

 it was, it apparently supplied something in the protoplasm of 

 Paramcecium that had not given out before, but had failed at 

 this particular time. Further, and more carefully-guarded ex- 

 periments, must now be undertaken in the hope of finding out 

 what these failures mean. 



Turning again to the controversy regarding " old age " in 

 Protozoa, it seems that we shall have to side with Weismann in 

 the contention that these organisms have the potential of end- 

 less existence, and this without conjugation. The five times 

 that the cultures of Paramcecium have been rescued at periods of 

 depression, justify the belief that they may be saved as many 

 times more, provided the time and patience required for such 

 work are not out of all proportion to the results gained. It 

 seems to be merely a matter of finding the right food, i. c., the 

 right chemicals. In nature, it is not improbable that the periods 

 of depression, which are experienced in the laboratory, would be 



