matter. In the first moment of secretion it forms 

 a thin yellowish milk, which thickens by degrees 

 as it loses its water. 



Respecting the Skin, and the parts connected 

 with it, our chemical information is hitherto very 

 imperfect. What we know is chiefly obtained 

 from accidental observations in tanning 1 and glue 



O c5 



making. The skin (or hide) changes by long boil- 

 ing into a glue, which is better and more tena- 

 cious in proportion as the skin is more difficult of 

 solution. Tanning consists in combining the 

 unchanged mass of the skin with tanning matter 

 from vegetables. This tanning matter, extract- 

 ed from various vegetables, often differs as much 

 in its nature, as the hides of different animals ; 

 and from this circumstance, the results will vary 

 according to the vegetable, Hvhich has been used 

 in the tanning process. Skin requires a certain 

 preparation previous to tanning. The object of 

 which is, by means of a liquid, to penetrate and 

 widen all the cells of the hide, in order to open 

 a sufficient space for the reception of. tanning 

 matter. Weak alkalies have a better effect here 

 than water, and acids succeed even better than 

 alkalis. Vegetable acids are prefered to mineral. 

 The quantity of acid in the water, with which 



