CHAPTER XVIII. 



BUTYRIC ACID FERMENTATION AND ALLIED 

 DECOMPOSITION PROCESSES. 



113. Anaerobiosis. 



THE first mention of the fact that butyric acid, discovered by 

 Chevreul in 1814, can also be produced by fermentation, was 

 made by R. MARCHAND (I.) in 1840, in connection with his 

 researches on the composition of the milk of the South American 

 cow-tree (Galactodendron americanum). In the following year 

 Noellner described, under the name of pseudo-acetic acid, a sub- 

 stance which he had found to result from the spontaneous decom- 

 position (fermentation) of calcium tartrate, and which was then 

 recognised by Berzelius as a mixture of butyric and acetic acids. 

 Two years later TH. PELOUZE and A. GELIS (I.) observed that the 

 lactic fermentations instituted by them did not progress satisfac- 

 torily, butyric acid and considerable quantities of hydrogen being 

 produced. In following up this observation they formulated the 

 recipe, still current in many text-books on chemistry, that to start 

 butyric acid fermentation a solution containing about 10 per cent, 

 of sugar should be mixed with chalk and a little cheese, and left 

 to stand at 25-3o C. 



These observers did not endeavour to follow the progress of 

 this fermentation more minutely, as their attention was entirely 

 devoted to the new fermentation product ; the only remark they 

 make is that the butyric fermentation is not set up at once in their 

 method, but is preceded by a lactic fermentation, " without its 

 being possible to influence the progress thereof." It was naturally, 

 far from the thoughts of Liebig's former fellow-worker at Giessen 

 to attribute the decomposition to the activity of living organisms. 



The discovery of the true state of the case was made in 1861 

 by PASTEUR (VIII.), who showed that two successive processes 

 are here involved : first, the conversion of sugar into lactic acid 

 or calcium lactate, and afterwards the transformation of the lactate 

 into butyrate. He demonstrated that each of these changes is due 

 to a special ferment, of which the second is the only one we have 

 to deal with now. The microbe (2 \L broad and 2-15 p long) 

 causing butyric fermentation, and which we now recognise as a 

 bacillus, was regarded by Pasteur, not as a plant, but as an animal, 

 one of the infusoria, because it was observed to possess powers 



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