290 L. D. BUSHNELL 



B. mesentericus than with B. subtilis. The very small amount of 

 air remaining in these tubes apparently has no influence upon 

 the amount of growth. There were relatively no more organisms 

 present in tubes merely sealed and with 25 per cent volume of air, 

 that there were in those tubes which were exhausted and with 

 but 1 per cent of the volume of air. We believe that the organ- 

 isms in the tube exhausted to 685 mm. were under as completely 

 anaerobic conditions as it is possible to obtain. 



According to Bitting and Bitting (1916) an ordinary tin can 

 shows a vacuum of about four inches of mercury when exhausted 

 at a temperature of 130°F. and tested at 85°F, 



We may conclude from the results obtained, that the degree 

 of vacuum plays no part in the destruction of the spores of these 

 two organisms. "V\1ien one per cent of salt is present, there may 

 be a sUght decrease in the twenty-seven days of incubation. 

 This is somewhat more marked in higher vacuum than in the 

 lower, but the differences are not marked. In the presence of 

 larger amounts of salt, there appears to be an actual increase in 

 the number of viable bacteria. This is apparently not due to 

 accidental conditions, since we have made numerous parallel 

 determinations and find that the averages of those determined 

 at the end of the incubation period are two or three times as 

 high as the number added. Why there should be a decrease in 

 the presence of 1 per cent, and an increase in the presence of 4 

 per cent salt we are unable to say. Of course there is considerable 

 variation in the determinations, but the averages indicate a real 

 increase. 



Experiment III. This experiment was set up parallel with that 

 of experiment II, except that varying amounts of acid were added 

 to the broth. The organisms were treated in the same way as 

 those in the last experiment, except that they were suspended in 

 acid broth after heating to kill the vegetative forms. The tubes 

 were incubated at 37°C. for twenty-three days for B. subtilis and 

 twenty-two days for B. mesentericus. The results are shown in 

 tables 4 and 5. 



Apparently B. subtilis spores are more sensitive to acid than 

 those of B. mesentericus. The degrees of vacuum had no influence 



