266 BACTERIA IN TANNING. 



deposited in the intercellular spaces in the hide, which is thus 

 rendered somewhat brittle and less pervious to the tanning liquor. 

 This carbonate precipitate is removed by steeping the hides in a 

 pickle or " bate " consisting principally of a mixture of bran, barley 

 groats, and the excrement of various animals (dogs, fowls, pigeons, 

 &c.) in a state of acid fermentation. The chief, if not the sole 

 raison d'etre of this process, which has been gradually developed 

 through tentative experiments alone, has only been brought to 

 light in recent years. The first progressive step consisted in the 

 discovery, by AUG. FREUND (I.) in 1871, that lactic acid is the 

 chief product of the spontaneous acid fermentation of wheat bran. 

 This explained the favourable result of the bating of lime-slackened 

 hides, the calcium carbonate being converted into the soluble cal- 

 cium lactate, and thus washed out of the hides. 



Pickling, however, effects a second and remarkable alteration 

 in the hide, causing it to swell up ("plump") to almost double its 

 former thickness, thus loosening the cellular tissue and facilitating 

 the subsequent penetration of the tannin. In order to make the 

 most of this advantage, it is generally the custom to pickle even 

 the hides that have been unhaired by the sweating process, and 

 which consequently do not contain any lime that needs to be 

 removed. The object in this case is to plump the hides, i.e. cause 

 them to swell up, and this explains the term "plumping soak" 

 applied to this acid liquor. This expansion of the skin is due to 

 the action of the gases liberated in the fermenting liquor. The 

 reactions occurring in this process are very diversified ; as might 

 be expected from the large number of bacterial species present in 

 the bran itself and in the added faecal matter. Of these organisms, 

 such as attack the carbohydrates develop most vigorously, these 

 substances being present in large amount. 



J. T. WOOD and W. WILLCOX (I.) described one species of 

 this kind and gave it the name of Bacterium furfuris. The starch 

 in the bran is hydrolysed and converted into glucoses by an 

 enzyme, cerealin isolated from bran extract by J. T. WOOD (I.) 

 and these sugars are then acted upon by the bacteria in question, 

 organic acids and considerable quantities of gas being produced. 

 In a'sample examined by WOOD (II.), i litre of the fermented bate 

 contained 0.8 gram of lactic acid, 0.2 gram of acetic acid, 0.03 

 grain of formic acid, and o.oi gram of butyric acid. The dis- 

 engaged gas was found, in different experiments, to consist of 

 22-42 per cent, of CO 2 , 28-53 per cent, of H, 24-26 per cent, 

 of N, and 1-4. per cent, of O, the percentage of carbon dioxide 

 increasing as fermentation progresses. This fermentation is at- 

 tributed by Wood and Willcox to the said bacterium, which they 

 describe as short rods 0.7 p long and 1.3 \i broad united to form 

 chains, but not, so far as they could ascertain, producing endo- 

 spores. The cell-walls exhibit a tendency to swell up. The 

 organism is incapable of attacking solid or dissolved starch, and 



