62 MEMBRANES PROBABLY EXERT 



effect. It is hardly necessary, particularly to point 

 out that an explanation of the action of purgatives in 

 general cannot be included in the above-described 

 action of saline solutions on the organism. The 

 example which has been given is intended to illus- 

 trate a physical property common to a large number 

 of salts, and apparently independent of the nature 

 of the acid or base of the salt ; for chloride of 

 calcium, chloride of magnesium, bitartrate of potash, 

 tartrate of potash and soda, phosphate of soda, and 

 certain doses of tartar emetic, shew the same action 

 as sea salt, Glauber salt, and Epsom salt, although 

 the bases and acids in these different salts are not 

 the same. 



Organic Solutions of cane sugar, grape sugar, sugar of 



milk, and gum, exhibit, when separated from water 

 by an animal membrane, phenomena similar to 

 those exhibited by the above-named solutions of 

 mineral salts, without causing in the living body a 

 purgative action, when of equal concentration. The 

 cause of this difference may be that the mineral 

 salts, in their passage through the intestinal canal, 

 and through the blood, are not essentially altered in 

 their composition, while these organic substances, in 

 contact with the parietes of the stomach, and under 

 the influence of the gastric juice, suffer a very rapid 

 change, by which the action which they have out of 

 the body is arrested. 



influence Since the chemical nature and the mechanical 



of mem- 

 branes on character of membranes and skins exert the greatest 



secretions. 



