156 A MANUAL OF BACTERIOLOGY 



ing solutions of mannite, glucose, sucrose, lactose, 

 starch, glycerol, and calcium glycerate. It has no 

 fermentive action on dulcite, the isomer of mannite, 

 which thus furnishes a very striking instance of the 

 selective power of microbes between the most closely 

 allied isomeric bodies. The products of the fer- 

 mentation of the above-mentioned compounds are 

 essentially alcohol and acetic acid, with a small and 

 variable proportion of formic acid, together with a 

 trace of succinic acid. Frankland l represents the 

 decomposition of glyceric acid (calcium glycerate) by 

 this microbe as follows : 

 5C 3 H 6 4 = C 2 H 5 OH + 4CH 3 COOH + H 2 + 3H 2 



+ 5C0 2 . 



The alcohol and acetic acid are produced approxi- 

 mately in the proportion of one molecule of alcohol 

 to four molecules of acetic acid. 



Bacillus lutyricus. This is the microbe of the 

 butyric fermentation ; and it is found in the cells of 

 laticiferous plants, in milk, and in decaying-plant 

 infusions, etc. B. butyricus is morphologically like 

 B. subtilis, but distinguished by the fact that at 

 certain times it contains starch in its cells. It 

 measures from 3 to 10 //, in length and 1 p in 

 breadth : it frequently forms chains, and gives rise 

 to well-developed spores. When spore-formation is 

 about to take place the protoplasm of the cell 

 becomes granular, and at certain points gives rise to 

 oval spores. This microbe grows on gelatine-plates, 

 in the deeper layers of the medium, as yellow or 

 brown colonies of a granular appearance ; and ulti- 



i Journal of Chemical Society, 1891, p. 81. 



