534 PHILOSOPHICAL TRANSACTIONS. [aNNO 1795. 



belief, that very dissimilar structures in the more perfect animals are endowed 

 with this principle, since the actions of the smaller arteries, as well as of the 

 absorbent vessels, must be referred to it. 



To ascertain whether any such action could be demonstrated in the membranes 

 of the quadruped, I made the following experiments. 



These experiments were made on the internal membrane of the urinary bladder 

 of a dog, which, in consequence of the animal dying a violent death, was in a 

 very contracted state ; the whole of its contents having been expelled in the act 

 of dying. The method I have adopted to ascertain the muscular power of this 

 membrane, is similar to that taken by Mr. Hunter in his very ingenious investi- 

 gation of the structure of blood-vessels, which was laid before this Society ; the 

 same mode being equally applicable to the present subject.* The bladder was 

 carefully laid open, and a portion of its internal membrane, which was corrugated 

 into folds, was dissected off. This portion was spread out, so as to be com- 

 pletely unfolded ; it was then laid on a piece of plate glass wetted, to prevent, as 

 much as possible, any friction ; its exact length, in this contracted state, was 

 A of an inch ; it was now stretched out, and found to be If inch, on being left 

 to itself, it contracted so as to be only 1 inch, so that in this state it had gained 

 -I- of an inch, which must have been lost by some action in the living body, and 

 entirely independent of its elasticity. This portion of membrane then had 2 

 powers of contraction, 1 which was muscular, and equal to f of an inch, 

 the other elastic, and equal to -f- of an inch. Another portion of the same 

 membrane, ^ an inch long and a broad, was treated in the same way, and its 

 muscular contraction was found to be -i- of an inch, that from elasticity a of 

 an inch. A 3d portion of membrane i of an inch long, and -f broad, was 

 ascertained to have contracted -2- of an inch by its muscular power, and f from 

 its elasticity. 



It is necessary to mention, that the muscular contraction in this membranous 

 structure, is very readily overcome, since this is almost self-evident ; that circum- 

 stance however must be particularly attended to in making similar experiments. 

 The internal membrane of the urethra we know to be capable of contracting, as 

 spasmodic strictures are formed in that canal. This membrane, when dried and 

 examined in the microscope, has not the same appearance as the coats of the hy- 

 datid ; but the whole is a congeries of vessels forming a net-work. We must 

 'therefore suppose that the action is in these very minute vessels. 



From these experiments and observations, membranous structures are found 

 to exert an action hitherto denied them ; and it is equally evident that this prin- 

 ciple is applied to the purposes of the animal economy in a more extensive man- 



♦ Mr. Hunter's experiments on the arteries of the horse are published in his treatise on the Blood, 

 Inflammation, and Gun-shot Wounds. — Orig. 



