ON BACTERIOLOGY IN ITS EELATIONS TO CHEMICAL SCIUNCE. 447 



by the B. orthobutylicus, and has found that in all cases the products 

 were qualitatively the same — viz., acetic and butyric acids, normal 

 butylalcohol, carbonic anhydride, and hydrogen. 



I do not, however, for a moment suppose it likely that one and the 

 same organism will decompose all substances, so as to form the same 

 products ; but it is suiEciently remarkable that the same products should 

 be obtained from such comparatively different parent substances, a 

 phenomenon which is most probably explicable by the assumption that 

 the several substances are, in the first instance, broken down into 

 some intermediate substance which then undergoes further transforma- 

 tion. 



Thus, probably the fermentability of bodies depends upon their being 

 able to yield such intermediate substances with facility. A substance 

 that doubtless plays an important part as an intermediary in such fer- 

 mentation decompositions is lactic acid, which is known, indeed, to be 

 capable of yielding a number of different products under bacterial action — 

 e.g., valerianic, butyric, propionic, and acetic acids, besides butyl and ethyl 

 alcohols. In this connection it is worthy of note also that the only sugars 

 which are capable of undergoing fermentation by yeast are those which 

 contain three or some multiple of three atoms of carbon in the molecule ; 

 moreover, even towards the bacterial ferments, with their more catholic 

 tastes, the carbon compounds containing such a tri-carbon nucleus appear 

 to offer peculiar facilities for attack. That intermediate reactions of 

 various degrees of complexity take place in these fermentative decom- 

 positions again is shown by the several kinds of lactic fermentation, to 

 which I will refer presently. 



In these fermentation phenomena formic acid appeal's to play a very 

 important part ; the presence of this substance among fermentation pro- 

 ducts has been observed by a number of investigators. It is frequently 

 mentioned as occurring, generally in small quantities, by Fitz, and simi- 

 larly by Grimbert, in the butyric fermentations, to which I have already 

 referred. In my experiments, however, I have found that the amount of 

 this formic acid may be very greatly increased by special conditions. 

 Thus in those fermentations conducted in flasks closed only with cotton- 

 wool plugs the proportion of formic acid was generally only very insignifi- 

 cant, whilst in the case of fermentations carried on in closed vessels 

 provided only with a delivery-tube dipping under mercury for collecting 

 the evolved gases the proportion of formic acid produced was invariably 

 very considerable ; and, further, in these closed fermentations in which 

 the gases were collected I have always found that the carbonic anhy- 

 dride and hydrogen were evolved in approximately the proportions in 

 which they are present in formic acid — viz., equal volumes. In these 

 closed fermentations it was, moreover, found that the fermentation was 

 less complete than in the flasks plugged with cotton-wool only. Now it 

 has been shown by Duclaux (' Annales de I'lnst. Pasteur,' vi. [1892], 598) 

 that free formic acid is a powerful antiseptic, and it is highly probable, 

 therefore, that the production of this formic acid in the closed fermentations 

 is the cause of their being prematurely arrested by this toxic product. 

 Whether the formic acid is not produced at all when the fermentation 

 takes place in the open flask, or whether the organism is capable of de- 

 composing it in the presence of air under these circumstances, I have not 

 yet determined. Duclaux (loc. cit.) has shown that moulds are capable 

 of destroying free formic acid in the presence of air j but the action of 



