36 OUEEENT FOECE CHAP. rV. §. I. 



J-* of its weight of salt; and after placing it upon 

 a shilling with the bladder slightly moistened 

 externally, I bent a wire of zinc, so that while one 

 extremity rested on the shilling, the other might 

 be immersed about an inch in the water. By suc- 

 cessive examinations of the external surface of the 

 bladder, I found that even this feeble power occa- 

 sioned soda to be separated from the water, and 

 to transude through the substance of the bladder. 

 The presence of alkali was discernible by the appU- 

 cation of reddened litmus-paper after two or three 

 minutes, and was generally manifested even by the 

 test of turmeric paper before five minutes had 

 expired. 



" The efficacy of powers," continues Wollaston, 

 " so feeble as are here called into action, tends to 

 confirm the conjecture, that similar agents may be 

 instrumental in effecting the various animal secre- 

 tions which have not yet been otherwise explained." 



There is one circumstance connected with Woir 

 laston's conjectm'e which must be noticed, viz. the 

 idea that secretion depended upon, or is the effect of, 

 a power similar to that which exists in a voltaic 

 circle ; but it must be borne in mind, that the origin 

 of the power in the voltaic circle was not so com- 

 pletely understood at the time Wollaston published 

 his conjecture as it is at the present day; and 

 although he himself was an advocate for the opinion 

 that it depended upon chemical action, it never- 

 theless required the elucidation that it has subse- 



