STUDIES ON LIFE-HISTORY OF PROTOZOA. 197 



regular stimulus, with the general vitality under conditions of 

 an initial stimulus. The history of these experiments is shown 

 graphically in the diagram shown on page 198. 



On the first of January, all were in fairly good condition and 

 the division-rate was about the same for all. All showed a de- 

 cline in the latter part of February, and the rate of division rose 

 for all of them in March. At this time there was a sudden warm 

 period in which the temperature for that ten-clay period increased 

 3 degrees on the average and this apparently acted as a mild 

 stimulus. From this time on, however, the division-rate of the 

 hay-fed individuals began to fall, and as soon as this fact was 

 noticed, the beef treatment of the others was stopped. The hay- 

 fed individuals did not recover their vitality and their division- 

 rate continued to fall until finally stock and all died, apparently 

 worn out. The beef-fed individuals, on the other hand, continued 

 their high rate of division throughout the period of decline of their 

 sister-cells, and did not show signs of diminished vitality until the 

 first period in June. At this time, however, the rate fell very rap- 

 idly and the depression was clearly apparent in the daily records 

 (See Fig. i). The organisms at this time had not had beef- 

 extract since March and they were accordingly transferred to it 

 now with perfect confidence on my part that it would again prove 

 to be the "elixir of life " for the Paramcecium. This time, hoiv- 

 ever, it failed to give the looked-for result, and the animals con- 

 tinued to die at a rapid rate. Their appearance indicated that 

 their trouble was not the same as in the previous periods of de- 

 pression. Hitherto at such times the endoplasm appeared black 

 under the microscope from the large numbers of gastric vacuoles 

 with their food contents unchanged. At this time, on the other 

 hand, the endoplasm was clear and free from such food masses, 

 but the appearance of the protoplasm was singularly granular and 

 different from that of a healthy individual. All changes that had 

 proved beneficial before were now tried. These included not 

 only liver, various vegetable infusions and the like, but salts of 

 various kinds. Nothing seemed suitable for the organisms and 

 they died off at a faster rate than ever. When the last of the B 

 series, stock and all, died in the S^oth generation (June 16), and 

 the A scries became reduced to only 6 individuals in the 62Oth 



