268 BACTERIA IN TANNING. 



change, well known to all tanners, was first chemically investi- 

 gated by H. BRACONNOT (L), who, in 1832, discovered in soured 

 bark liquor an acid which as little was then known of the pro- 

 perties of lactic acid he considered to be a new, hitherto un- 

 discovered acid, and therefore named it " acide nanceique," after 

 the town of Nancy, where the discovery was made. This acid was, 

 however, quickly recognised byL. Gmelin as lactic acid. J. WLADIKA 

 (I.) in 1890 showed that volatile, as well as non- volatile, acids are 

 present in old spent bark liquors, the former consisting chiefly of 

 acetic acid and the latter of lactic acid. The reader will have no 

 doubt that the reduction of these acids (which are not present in 

 the "sweet" liquor) is attributable to the activity of micro- 

 organisms, which are here present in abundance, HAENLEIN (II.) 

 having found no less than 60,000 bacteria (along with a few 

 budding fungi) in the liquor prepared from, and corresponding to 

 i m.grrn. of, Silesian oak-bark. The acids are produced from the 

 saccharine constituents of the bark, a fact already evidenced by 

 the researches of B. KOHNSTEIN (L) and J. VON SCHROEDER (L), 

 who showed that in proportion as the sweet liquor becomes sour, 

 so the percentage of these sugary constituents decreases. In 

 practical working their initial quantity is found to be from 0.3 to 

 0.8 gram per litre. 



A fission fungus named Bacillus corticalis, and recognised as 

 an active participant in the souring of bark liquor, was dis- 

 covered by HAENLEIN (III.) in large quantities in sour pine-bark 

 liquor, as also in the fresh pine-bark. This microbe appears in 

 the form of short rods, 0.7-1 //, broad and one and a half to 

 twice these dimensions in length ; at the period of active repro- 

 duction the individual cells are connected into many-jointed 

 chains. The bacillus thrives on nutrient gelatin, nutrient agar- 

 agar, and slices of potato, and requires but very little nutriment. 

 Being able to withstand desiccation, it remains alive in bark, 

 where it is found in large numbers. It has a great affinity for 

 light, and grows more freely when illuminated than in the dark, 

 though it is still capable of performing its vital functions under 

 the latter condition. It thrives most vigorously at 3o-4o C., 

 and ceases to develop below 5 C. ; in habit it is facultatively 

 anaerobic, i.e. oxygen is not essential to its growth. Its most 

 important property, so far as we are now concerned, is its be- 

 haviour towards sugars, of which it acts upon dextrose as well as 

 saccharose and lactose, and produces, in addition to acids, a con- 

 siderable quantity of gas, composed (in one case investigated) of 

 95 per cent, of hydrogen and 5 per cent, of carbon dioxide. 

 Tannin is not attacked by this microbe, a fact confirmed by the 

 observation made by J. VON SCHROEDER and A. BARTEL (I.), that 

 the percentage of tannin in the liquors undergoes no alteration on 

 standing or during storage. 



The acidity of tanning bark liquors amounts to 0.25 gram 



