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. MARCHANB (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 substance which he 

 had found to result from the spontaneous decomposition (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 satisfactorily, 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 2 5 "-30 C. 



These observers did not endeavour to follow the progress of this fermentation 

 more minutely, as their attentio i 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, b it 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 trans- 

 formation 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 p. broad and 2-15 \t 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 of locomotion. Nevertheless he laid but little stress on this distinction, 

 the point being one of minor importance in comparison with the property he 

 recognised in this " vibr ion butyrique" viz., the faculty of existing without air. 

 This observation formed one of the main supports on which this gifted philosopher 

 founded his theory of fermentation, mentioned in 16, and with regard to which 

 a few additional remarks will now be made. 



At present we have first to consider the said peculiarity by itself, irrespective 

 of the resulting decomposition effected in the nutrient medium. Creatures 

 requiring oxygen for the continuance of their existence are termed aerobiontes, 

 whilst the term anaerobiontes, or, shortly, anaerobes, is applied to creatures capable 

 of development in the absence of this gas. A distinction is drawn between two 

 sub-groups, viz., strictly anaerobic organisms, i.e. such as can live only in an 



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