BARBER: HEREDITY IN CERTAIN MICRO-ORGANISMS. 29 



have been as nearly as possible under the same conditions be- 

 fore use. 



Examination of the cultures remaining in the bulbs after 

 the close of the experiment was frequently made, and no 

 signs of contamination found. 



In order to eliminate possible error due to differences in the 

 fermentation tubes used, the tubes of a pair were sometimes 

 changed after a test, and in a new test each was made to con- 

 tain the organism previously grown in the other. Both tubes 

 were kept in the incubator at the same temperature during 

 an experiment, and observation was made at the same time 

 of both, and without opening the inner glass door of the in- 

 cubator, 



A possible source of error lies in the fact that there was no 

 maximum recorder in either type of tube. This source of 

 error was largely eliminated by making frequent observations 

 up to the time of maximum pressure. 



In the table below, the figures in the second and third 

 columns represent the maximum volume of gas formed in the 

 fermentation tubes of type No. 1, and the the maximum 

 pressure of gas recorded by the mercury column in type No. 

 2. The hours and average temperatures are reckoned from 

 the time when the apparatus attained the temperature of tne 

 incubator until the pressure had reached its maximum. 



Table IV. — Fermentation tube No. 2. Fermentation under pressure. 



