196 BA CTERIOLOG Y. 



nature and quantitative relations of these gases Smith l 

 recommends the following procedure : " The bulb is 

 completely filled with a 2 per cent, solution of sodium 

 hydroxide (NaOH) and closed tightly w r ith the thumb. 

 The fluid is shaken thoroughly with the gas and allowed 

 to flow back and forth from bulb to closed branch and 

 the reverse several times, to insure intimate contact of 

 the CO 2 with the alkali. Lastly, before removing the 

 thumb all the gas is allowed to collect in the closed branch, 

 so that none may escape when the thumb is removed. 

 If CO 2 be present, a partial vacuum in the closed branch 

 causes the fluid to rise suddenly when the thumb is re- 

 moved. After allowing the layer of foam to subside 

 somewhat the space occupied by gas is again measured, 

 and the difference between this amount and that meas- 

 ured before shaking with the sodium hydroxide solution 

 gives the proportion of CO 2 absorbed. The explosive 

 character of the residue is determined as follows : the 

 thumb is placed again over the mouth of the bulb and 

 the gas from the closed branch is allowed to flow into 

 the bulb and mix with the air there present. The plug 

 is then removed and a lighted match inserted into the 

 mouth of the bulb. The intensity of the explosion varies 

 with the amount of air present in the bulb." 



Durham's Fermentation - tube. Durham employs 

 a convenient modification of the ordinary fermenta- 

 tion-tube, which is constructed in the following 

 manner : test-tubes of about 10 or 12 c.c. capacity 

 are placed in an inverted position within a larger 

 test-tube, and the latter plugged with cotton in 

 the usual way and sterilized. (See Fig. 37.) The 

 small tube should fit loosely within the larger one. 



. cit., p. 196. 



