BIOLOGY OF BACTERIA. 55 



employed. They are filled with glucose bouillon, steril- 

 ized as usual, inoculated and allowed to grow. If gases 

 are formed, the bubbles ascend and the 

 gas accumulates at the top of the tube. 

 In estimating quantitatively, one must 

 be careful that the tube is not so con- 

 structed as to allow the gas to escape as 

 well as to ascend in the main reservoir. 

 For the determination of the nature 

 of the gases ordinarily produced, some 

 of which are inflammable and some not, 



mi i_ u r '^i i 11 FIG. 5. Smith's fer- 



Theobald Smith has recommended the raen tation-tube. 

 following methods: 



"The bulb is completely filled with a 2 per cent, so- 

 lution of sodium hydroxid (NaOH) and tightly closed 

 with the thumb. The fluid is shaken thoroughly with 

 the gas and allowed to flow back and forth from the 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 col- 

 lect 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 sud- 

 denly when the thumb is removed. 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 measured before shaking with the 

 sodium hydroxid solution gives the proportion of CO 2 

 absorbed. The explosive character of the residue is 

 determined as follows: "The cotton plug is replaced 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." 



7. Production of Odors. Of course, such gases as H 2 S 

 and NH 2 are sufficiently characteristic to be described as 

 odors. There are, however, a considerable number of 



