SPECIAL INDUSTRIAL FERMENTED PRODUCTS 655 



LEATHER * 



In the manufacture of leather, bacteria play a very important and 

 extremely interesting role. Success depends to a very great degree 

 upon the proper control of microorganisms during the various steps 

 of the manufacturing process. 



Most hides and skins are received at the tannery fresh with more or 

 less adhering blood and flesh. Hides from outlying districts or foreign 

 countries are received in the salted or dried states. 



The hides are first placed in water, in the so-called " soaking pits," 

 to remove the blood from fresh hides, the salt from salted hides and to 

 plump and soften the dried hides. Formerly "putrid soaks' 1 were 

 used. The liquid in these soaks had stood for a long enough period to 

 become swarming with putrefactive organisms. Much of the gelatin 

 of the hide was dissolved and often the grain of the hide was injured 

 by bacterial action. B. fluorescens liquefaciens, B. megatherium, 

 B. subtiliSj B. proteus mtlgaris, B. proteus mirabilis, were commonly 

 found in this liquid according to J. T. Wood.f None are beneficial to 

 the hide and most of them are harmful. If the water is changed fre- 

 quently there is less danger of putrefaction; Proctor recommends the 

 use of an antiseptic solution of 1:1000 sodium hydroxide or from i to 

 3 per 1000 of sodium sulphide to prevent bacterial growth during 

 soaking. 



The wool is often removed from sheep skins by bacterial action. 

 The hides are hung on racks in an air-tight room at 15 to 20. Wood 

 reports the following organisms to be active during this " sweating' 1 

 process: B. fluorescens liquefaciens, Bad. pilline, and a streptococcus. 

 These organisms secrete enzymes which dissolve the cementing sub- 

 stance at the roots of the wool permitting the wool to be easily removed. 

 It is difficult to check or control this process; usually some hides from 

 the " sweating stove " will be spoiled by too prolonged putrefaction. 

 Caustic sodium sulphide is used to a considerable extent to replace the 

 sweating process. 



The hair is removed from hides and calf skins by liming. The 

 hides are first placed in a lime pit consisting of water and slaked lime 

 that has been in use for some time. This old lime pit contains proteo- 



* Prepared by W. V. Cruess. 



t Wood, J. T: Bacteriology of the Tanning Industry, Journal of Soc. Chem. Ind., 1910, 666. 



