656 MICROBIOLOGY OF SPECIAL INDUSTRIES 



lytic bacteria which develop upon the gelatin and other nutrient mate- 

 rial dissolved from the hides previously treated. These organisms exert 

 an appreciable depilatory action and considerably increase the activity 

 of the lime. Some of this effect is due to ammonium salts and amines, 

 formed by the bacteria. Much of the bacterial effect can be duplicated 

 by adding ammonium sulphate. From this lime pit hides in time go to 

 pits containing new lime and thence to the beam where the hair is re- 

 moved by scraping. 



If the hide is for sole leather or other heavy leather it goes direct 

 to a dilute lactic acid or dilute mineral acid bath where the excess lime 

 is dissolved without removal of any appreciable amount of the hide 

 substance needed to give rigidity to the leather. 



Soft leathers require a different treatment. Fine leathers such as 

 glove leather are usually given a puering treatment in which the skins 

 are placed in a dilute infusion of dog dung which has previously been 

 permitted to stand several days to develop the proper types of bac- 

 teria. Other skins are given a bating process in pigeon or hen dung 

 infusion or in a proprietary bating solution. The hen or pigeon 

 dung is prepared for use by soaking in warm water several days. Fer- 

 mentation and vigorous development of bacteria ensue. The ferment- 

 ing infusion is diluted with water and mixed with the skins in the 

 "bating wheel" which consists of a large wooden paddle wheel revolv- 

 ing in a tank of the bating liquor. In the puer and bate liquors the 

 lime is dissolved from the hides to some extent by lactic acid and also 

 through the action of amines and ammonium salts formed by the bac- 

 teria from proteins of the skins. Some of the intra-cellular substance 

 of the skin is dissolved. The skins become soft and pliable, i.e., "fall. " 

 The surface becomes slippery and the skin retains the imprint of the 

 finger if pressed between the thumb and ringer. Too prolonged bating 

 or puering results in pitting of the hide; in fact, it is possible to cause 

 the hide to go completely into solution by several days' bating at 

 37, the temperature ordinarily used in practice. 



Many attempts have been made to replace the dung infusions with 

 pure cultures. In cooperation with F. H. Wilson the writer isolated a 

 number of organisms from bate liquors. Most of these were of the 

 colon group; some of the proteus group. The colon group of organisms 

 gave good results in pure culture when grown in dilute milk (diluted 

 i : 10) with water or in dilute sugar solutions. The milk or other sugars 



