K.— BOTANY 2ii 



specific chemical action. It appears probable that it was this that gave 

 Pasteur his first interest in ferments. ' If I place one of the salts of race- 

 mic acid, paratartrate or racemate of ammonia, for instance, in the ordinary 

 conditions of fermentation, the dextro-tartaric acid alone ferments, the 

 other remains in the liquor. I may say, in passing, that this is the best 

 means of preparing laevo-tartaric acid. Why does the dextro-tartaric 

 acid alone become putrefied ? Because the-ferments of that fermentation 

 feed more easily on the right than on the left molecules.' 15 Pasteur called 

 the mould Penicillium glaucum ; but it is still necessary to emphasise 

 that this name as generally understood merely denotes a green Penicillium 

 and ' greenness has no more significance in predicting biochemical 

 ability of a Penicillium than bayness of a horse in judging his speed in a 

 horse race ' ; it is of no greater significance in taxonomy. 



The other necessary step was made also by Pasteur when in i860 he 

 used a synthetic medium with the ash of yeast as a basis. This was 

 followed by the laborious work of his pupil, J. Raulin, who replaced the 

 yeast-ash with salts necessary for the maximum growth of Aspergillus 

 niger. 



Another of Pasteur's favourite pupils, P. van Tieghem, studied the 

 formation of gallic acid from tannin (1867). This acid had been dis- 

 covered in 1786 by C. W. Scheele in decomposing gall-nuts. In the pro- 

 duction of gallic acid, gall-nuts, chiefly of Chinese origin, are powdered, 

 mixed with water and left at 20 to 25 C. for eight to ten days until they 

 are mouldy. Most of the tannin (gallotannic acid) is converted into 

 gallic acid. Van Tieghem found that the active agent in the fermentation 

 is Aspergillus niger ; the high concentration of the tannin apparently 

 prevents the development of other moulds. 



Calmette patented a process in 1904 for the production of gallic acid 

 by fermenting clear tannin extract with ' Aspergillus gallomyces,' the fungus 

 being kept submerged by means of a mechanical agitator and by intro- 

 ducing large quantities of sterile air. 



Gallic acid is a mordant and a constituent of inks. At the beginning of 

 the War it was used in the production of gallocyanine with which American 

 sailors' uniforms were dyed. 



Many fermentation reactions are not so simple as they appear at first 

 sight. We know the constitution of the original substance and the final 

 products. It seems certain that the intermediate stages are common 

 in these reactions, but what these are is usually a matter of conjecture 

 and discussion. The time-honoured equation proposed by Gay-Lussac 

 for the fermentation of sugar by yeast gives the main facts but takes no 

 note of possible intermediate stages, and, moreover, does not account for 

 the occurrence of glycerol which Pasteur showed, so early as 1858, 16 

 might occur in amounts up to three per cent, of the fermented sugar. The 

 uses of glycerol (glycerine) are manifold, but the chief one is in the manu- 



16 The Life of Pasteur, by R. Vallery-Radot. 



16 ' I find that alcoholic fermentation is constantly accompanied by the pro- 

 duction of glycerine ; it is a curious fact. For instance, in one litre of wine 

 there are several grammes of that product which had not been suspected.' — 

 Letter to C. Chappuis. 



