132 



MANUAL OF BACTERIOLOGY. 



property of splitting up organic compounds with the formation 

 of various gaseous products. Perkins* has found that the 

 power of thus breaking up sugars with the formation of gas- 

 eous products may be lost in whole or in part by modification 

 of environment. In some cases the power would seem to be 

 permanently lost, in others it may be recovered again. This 

 observation makes it necessary to interpret with great caution 

 the results of fermentation tests as a specific means of differen- 

 tiation between organisms which 

 are otherwise alike. It is important 

 to bear this fact in mind particularly 

 in the diagnosis of the members of 

 the colon group. Carbon dioxide, 

 hydrogen sulphide and nitrogen are 

 among the better known gases that 

 may be formed. The odors that 

 arise from cultures and that are so 

 characteristic of putrefactive pro- 

 cesses depend upon the develop- 

 ment of gases, or a mixture of 

 gases, of considerable complexity. 

 The bacillus aerogenes capsulatus 

 leads sometimes to the formation 

 of gas in the organs of the human 

 cadaver within a short time after 

 death. Theobald Smith intro- 

 duced a valuable means of differentiating species of bacteria 

 based upon their power of forming gas in media containing 

 different sugars, or in their inability to do so. Bouillon con- 

 taining I per cent, of dextrose (or lactose, etc.) is the culture- 

 medium advised. The test is best conducted in a U-shaped 

 tube, closed at one end, and at the other end provided with a 

 bulb (Fig. 48). The tube is stoppered with cotton, sterilized 



♦Perkins. Journ. Inject. Dis. Vol. 4 No. i, pp. 51-65. 



Fig. 48. — Fermentation-tube. 



