134 FOURTH REPORT — 1834. 



of the water. The perpendicular height of the remaining co- 

 lumn of water appeared to show that the contractile power' of 

 the artery was greater than the power which dilated it by fifteen 

 millimetres of mercury. We suppose, however, that little can 

 be concluded from this experiment respecting the quantity of the 

 contractile force of the artery in the living body. It is placed 

 in the experiment in very different conditions. Being forcibly 

 dilated between fixed points, its coats represent in the longitu- 

 dinal direction a series of elastic cords, M^hich are forced into 

 curves, and the whole effect is due in part to the recoil of these, 

 and in part to that of the circular fibres. 



The elasticitjr of arteries, which lasts after death until decom- 

 position takes place, differs from that vital exertion of it called 

 tonicity, which is soon extinguished. By means of the two, 

 particularly the latter, the artery always adapts itself to its con- 

 tents. In consequence of the latter alone, the artery is smaller 

 shortly after death than after the lapse of several hours. I know 

 of no experiments which satisfactorily indicate any rapid con- 

 traction of arteries, which can be referred to muscularity. Their 

 middle coat, in which that property has been supposed to reside, 

 has been shown by Berzelius to differ from muscle, in being 

 more elastic, in having less combined fluid, in being insoluble 

 in acetic acid, soluble in mineral acids, but not precipitable from 

 the solution by potass. Its fibre affords no trace of the trans- 

 verse stri;e which Hodgkin and Lister regard as a peculiar cha- 

 racteristic of muscle. 



The pulse, depending upon dilatation of the arteries from the 

 force of the left ventricle, has until lately been by many supposed 

 to be synchronous throughout the body. E.H.Weber, after 

 Soemmerring,Majendie, Stocks and Carlisle, has shown that it is 

 not exactly so ; and for the reason that the arteries are not rigid 

 tubes. The blood driven by the heart into elastic tubes, distends 

 them by an undulation which is progressive. The pulse, which 

 is the distension of the vessel, is synchronous only at equal di- 

 stances from the heart, and in arteries at considerable distances 

 from the heart follows its beat by one sixth or one seventh of a 

 second. 



Heart. — Poisseuille, in order to ascertain the force with which 

 the heart drives the blood into the aorta, has repeated some of 

 Hales's experiments in a more accurate manner. His appara- 

 tus consisted of a glass tube, bent into a semicircle, so that its 

 branches were parallel. The shorter of these was again bent at 

 right angles, and nearly to this level the parallel branches were 

 filled with mercury. What remained of the shorter still empty, 

 together with its horizontal portion, was filled with a solution of 



