BACTERIA IN THE INDUSTRIES 717 



tanning proper consists in subjecting the skins to prolonged immersion 

 in solutions made up according to a large variety of formulae — ^the 

 principle of all of which, however, seems to be found in the mixing of 

 various organic ingredients, such as bran-mash, oak-bark, and often dried 

 animal excreta, in which fermentation and acid production occurs. 

 According to Haenlein ' this acidification is the essential process by which 

 the leather is sterilized and rendered soft and pliable. This author has 

 described a microorganism. Bacillus corticalis, which he found regu- 

 larly present in fir-tree bark and to which he ascribes the acid fermenta- 

 tion occurring in tanning liquors in which this ingredient is employed. 

 Wood,^ who has worked extensively upon the subject, has attempted 

 with some success to substitute pure cultures for the old uncertain 

 chance mixtures employed. In spite of these investigations, however, 

 while we must acknowledge the probable importance of bacteria in the 

 tanning process, the subject is by no means upon a scientific or exact 

 basis. 



» Haenlein, Cent. f. Bakt. 11, i, 1895. 



2 Wood, Jour. Soc. Chem. Industry, 1895, 1899. 



