286 L. D. BUSHNELL 



In an attempt to determine why B. mesentericus predominated, 

 we undertook some experiments, using these two types. The 

 types used were isolated from jars of asparagus and were rapid 

 spore formers, although they had been grown in the laboratory 

 for more than a year. 



The thermal death point of the spores of the B. subtilis culture 

 used in these experiments was from ninety to one hundred and 

 twenty minutes in steam at 98°C.; for B. mesentericus eighty to 

 one hundred minutes. The time at which all are killed depends 

 to some extent upon the numbers present. 



For the experimental work, the organisms were grown upon 

 plain extract agar from four to six days. The growth was scraped 

 from the medium and suspended in a small amount of sterile 

 normal saline. This was shaken in a heavy walled bottle with 

 glass beads and filtered through sterile cotton to remove clumps. 

 The suspension was heated at 80°C. for twenty minutes to kill 

 the vegetative cells. 



Experiment 1 . In this experiment we wished to determine the 

 influence of different amounts of air upon the growth of the 

 organisms. The number of spores indicated in the table were 

 added to tubes of extract broth, 0.50 per cent N/1 acid to phenol- 

 phthalein pH 5.9. In this case the column of air above the 

 medium was about 5 cc. The tubes were exhausted to various 

 points and sealed. The results are shown in table 1. 



From this table we may conclude that there was sUght growth 

 of both organisms during fifty-one days incubation at room tem- 

 perature in the less exhausted tubes. 



Experiment II was conducted in order to determine the in- 

 fluence of varying amounts of salt and air upon the growth of 

 B. subtilis and B. mesentericus. In this case, known amounts of 

 air were left above the Uquid. 



An attempt was made to remove all possible traces of air from 

 the medium. To do this, the tubes were partially filled with a 

 known amount of broth to which varying amounts of salt had 

 been added. The tubes were then drawn out to a slender neck, 

 as close to the liquid as possible, and heated in a seamer for 

 fifteen minutes. The tubes were next cooled in cold water, and 



