This philosopher has shown that, when a fluid, as water, or a weak saline solution, is enclosed in an organised membrane, as a piece of bladder, or placed in a glass tube over which a piece of membrane is firmly tied, and immersed in a solution of sugar, the bladder or glass tube becomes rapidly emptied ; but if, on the contrary, the bladder or tube, be filled with syrup, and immersed in distilled water, the reverse takes place, the bladder becoming completely injected and turgid, and the tube filled with fluid; which, at last (if the tube be not too long), runs over.

From these facts, amongst many others, M.

Dutrochet was inclined to draw the following deductions: — 1.

That, when a fluid of low specific gravity, enclosed in an organic membrane, is immersed in one of greater density, the membrane becomes rapidly emp- tied, in consequence of a current being set up from the lighter to the denser fluid (from within and without) ; and, 2, that, when a dense fluid is enclosed in a membranous reservoir, and immersed in a fluid of a lower specific gravity, a current is set up, whereby the membrane becomes distended by a sup- ply of fluid from without.

The exceptions to these two rules are very few, and may at present be set out of the question.