194 BACTERIOLOGY. 



very small cavities containing the gas that has re- 

 sulted. 



This property of fermentation with evolution of gas 

 is of such importance as a differential characteristic 

 that considerable attention has been given to it, and 

 those who have been most intimately concerned in the 

 development of otir knowledge on the subject do not 

 consider it sufficient to say that the growth of an organ- 

 ism " is accompanied by the production of gas-bub- 

 bles," but that under given conditions we should deter- 

 mine not only the amount of gas or gases produced 

 by the organism under consideration, but also their 

 nature. For this purpose, Smith 1 recommends the 

 employment of the fermentation-tube. This is a tube 

 bent at an acute angle, closed at one end and enlarged 

 with a bulb at the other. At the bend the tube is 

 constricted. To it a glass foot is attached so that 

 the tube may stand upright. (See Fig. 36.) To fill 

 the tube, the fluid (it is used only with fluid media) 

 is poured into the bulb until this is about half full. 

 The tube is then tilted until the closed arm is nearly 

 horizontal, so that the air may flow out into the bulb 

 and the fluid flow into the closed arm to take its place. 

 When this has been completely filled sufficient fluid 

 should be added to bring its level within the bulb just 

 beyond the bend, and the opening of the bulb plugged 

 with cotton. The tubes thus filled are then to be ster- 

 ilized. During sterilization they are to be maintained 

 in the upright position. Under the influence of heat the 

 tension of the water-vapor in the closed arm forces most 

 of the fluid into the bulb. As the tube cools, the fluid 



1 An excellent and exhaustive contribution to this subject has been 

 made by Theobald Smith in the Wilder Quarter-Century Book, Ithaca 



N. Y., 1803. 



