6o LABORATORY BACTERIOLOGY 



EXERCISE XXIV 



STUDY OF THE GAS PRODUCTION BY BACTERIA 



92. The knowledge of the powers of a given species of 

 bacteria to produce gas when grown in a medium containing 

 sugar is quite important. It is desirable to determine both 

 the quantity of gas and its relative composition. Chemical 

 analyses have shown that, in all cases tested, the gas resulting 

 from the fermentation of the sugar consists of a mixture of 

 hydrogen (H) and carbonic acid gas (CO2) with mere traces 

 of other gases. It is important to know also the quantity of 

 gas produced with the various sugars, especially glucose, lac- 

 tose, and saccharose. To determine simply whether an organ- 

 ism will prodiice gas it is only necessary to inoculate it into 

 tubes of liquid agar containing the various sugars ; but if the 

 quantity of gas is to he determined, the fermentation tube is 

 the most convenient apparatus to use. In some cases the 

 gks formation is one of the most striking differential properties, 

 as will be seen in the study of hog-cholera and typhoid bacilli. 



References. — For a discussion of the gas production and use 

 of the fermentation tube, see Smith, Wilder Quarter-century Book, 

 1893, p. 187 ; for the chemical formulae, see Novy, Laboratory Work 

 in Bacteriology, 1899. 



93. Work for this Exercise. — Examine and describe the 

 cultures in the glucose and plain agar inoculated in Exercise 

 XXII. Note the approximate size and number of gas bubbles 

 in the glucose agar, and explain the cause of difference in the 

 number of bubbles in the two agar cultures. 



Examine the fermentation tubes, and indicate the quantity 

 of gas and the ratio of gas to liquid m the closed branch. 

 Determine the ratio of CO^ to H in the gas. 

 In studying these cultures they should be examined each 



