154 MICROBIOLOGY 



f action 



C H 12 O + | of bac- = C 4 H 8 O 2 -f-2CO 2 +4H . . H/CO 2 = 50/50 



( teria 

 (Glucose) Butyric acid 



( action 



CH 12 6 + | of bac.- C 4 H 10 O+2CO 2 +H 2 O.'.H/C0 2 = 0/100. 

 I teria 



(Butyl alcohol) 



The percentage of C0 2 and H in the gases formed by many 

 bacteria especially the colon group vary, but for each species 

 a ratio between H and C0 2 is fairly constant. Smith l con- 

 sidered the gas formation and gas production as important 

 factors in identifying species. 



In order to test the production of a gas, a culture medium 

 composed of glucose-agar containing about 1 per cent grape- 

 sugar may be used. At the end of one to twelve hours in the in- 

 cubator (or twenty- four hours room temperature) the agar 

 will contain a greater or less number of gas bubbles. For the 

 determination of the quantity and kind of gas produced by a 

 given microorganism the fermentation tube recommended by 

 Theobald Smith is the best. This is a bent tube, constricted 

 greatly at its lowest portion, supported upon a glass base. 

 The tube is filled with a bouillon containing 1% glucose (or 

 other sugar) which has been sterilized in the steam sterilizer. 

 It is inoculated with a culture of the organism in question, 

 and observations made : 



1. If there is a turbidity produced in the open bulb it 

 indicates the presence of an aerobic species ; if this clouding 

 occurs only in the closed arm, while the open bulb remains 

 clear, it is an anaerobic species. 



2. The quantity of gas produced daily should be marked 

 on the upright arm ; if the tube is graduated a note of it is 

 taken and the percentage calculated on the fourth to sixth day 

 after gas production has ceased. 



3. A rough analysis of the gas produced may be made 

 as follows: Having designated by a mark on the tube the 



Smith. Wilder Quarter Century Book, 1893, p. 187. 



