VEIN. 



1385 



Holler * denies that they are endowed with 

 irritability. It is now placed beyond all ques- 

 tion that veins are endowed with vital contrac- 

 tility, and that it exists in them in two distinct 

 and entirely separate forms first, as a rlii/th- 

 mical contraction, similar to wh:it occurs in the 

 cardiac cavities ; and secondly, as that peculiar 

 slow and prolonged contraction which is known 

 as tonicity, and which in so striking a degree 

 exists, and exists alone, in arteries, the 

 former occurring in a small portion of the 

 venous track, the latter pervading nearly the 

 entire venous system. To the establishment 

 of this last physiological fact, we are mainly 

 indebted to Professor Kb'lliker. 



Venous rythmical contraction in man and 

 mammalia generally occurs only in the im- 

 mediate neighbourhood of the heart, but in 

 cold-blooded animals it extends a considerable 

 distance along the venous trunks. Flourensf 

 was the first to describe it in the frog, where 

 it has frequently been since witnessed ; and 

 Miiller has observed that the venous trunks 

 of the frog continue to contract even after 

 the removal of the heart and the auricle. 



Nysten has witnessed contraction of the 

 upper part of the vena cava in fish ; and 

 Wedemeyer has observed the same in other 

 cold-blooded animals. According to Miiller 

 the rhythm of the veins in frogs occurs just 

 previous to that of the auricle, and the rhythm 

 of the auricle before that of the ventricle, and 

 the rh\thm of the aortic bulb follows the 

 ventricular : there are four successive con- 

 tractions, of which that of the veins is the 

 first. 



In mammalia the venous contraction is 

 almost synchronous with the auricular. I 

 have frequently witnessed it in vivisect 

 animals rabbits, kittens, &c. ; and it exists 

 in the pulmonary veins as well as in the 

 cava?. It is only in the immediate neigh- 

 bourhood of the auricles that the veins 

 contract, doubtless just so far as the cardiac 

 muscle is prolonged into the venous tissues. 

 The rhythm appears to commence upon the 

 vein and pass forward upon the auricle. 

 This vascular rhythm, existing in a high degree 

 in the lower vertebrata, and diminishing in 

 the higher, would appear, in man, to be tiie 

 last remnant of the tubular heart seen in the 

 in vertebrata. 



It appears very probable that the contrac- 

 tion of the veins' close to the auricles may be 

 of assistance in the economy of the heart's 

 action. If it be recollected that the auriculo- 

 venous orifices are not guarded by valvular 

 apparatus, it will be difficult to explain how, 

 when the auricles contract, the blood is pre- 

 vented from flowing back into the patent 

 veins : may not this be prevented to a 

 certain extent by the contraction of the 

 veins, which thus constitute a sort of sphincter? 

 This rhythmical action of the veins must in no 

 way be confounded with that peculiar venous 



* Sec. Mem. sur les part, sensibles ct irritables : 

 anil Elem. Phys. lib. ii. p. 1-'<J. and lib. vi. p. 125. 

 f In Annales des Sciences Natur. torn, xxviii. p. C5. 



pulsation which exists in certain forms of 

 disease. Venous tonicily has lately been esta- 

 blished by Kolliker*, and his physiological ex- 

 periments have been based upon and fortified 

 by the most conclusive anatomical discovery 

 viz. the demonstration of unstripcd muscu- 

 lar fibre in the walls of veins. 



Professor Kolliker's experiments were 

 made upon the veins of a leg immediately 

 after amputation; and the aent of muscular 

 excitation was an electromagnetic apparatus. 

 " The vena saphena minor was touched in 

 the fossa poplitea, on the lower part of the 

 leg and on the foot ; the vena saphena magna 

 on the lower part of the leg and dorstun 

 peclis. A few seconds after the application 

 of the wire, contraction took place ; at the 

 end of a minute the parts touched contracted 

 so much, that the blood that they contained 

 in large quantities was pressed out, until the 

 vessel had the appearance of a white cord. 

 On smaller veins of the skin, the effect was 

 not so rapid or so powerful." 



" Three applications of the wire had no 

 effect or. the vena poplitea, but it was already 

 very flaccid and empty before the experiment. 

 The vena tibialis postica was empty by con- 

 traction in a minute." 



The irritability endured in the veins for un 

 hour and fifteen minutes, being somewhat 

 longer than in the arteries and lymphatics, 

 and shorter than in the muscles. 



This contractile power in veins is of that 

 peculiar character which has long been known 

 to exist in arteries : it is slow, gradual, and 

 persistent, and by it the vessel is braced up 

 and set at a given calibre. This contractility, 

 combined with the elasticity of the vessel's 

 walls, is the antagonist to the distending 

 force of the blood within the vessel. 



I have frequently noticed in animals ex- 

 amined during life, that the large venous 

 trunks are of greater calibre than when 

 viewed after death : that whilst the blood 

 flows on through the vessel, it is distended to 

 a larger size than when from exudation and 

 other causes the quantity of distending fluid 

 is diminished; just as at each jet of blood pass- 

 ing through an artery the tube is distended, 

 in opposition to its contracted state after 

 death, the explanation being undoubtedly 

 this, that immediately after death the vein- 

 muscle becomes affected with cadaveric 

 rigidity, and this being unopposed by the 

 distending blood, contracts the vessel to a 

 calibre less than that which it could hold 

 whilst the contraction was opposed by the 

 distending force of the circulating fluid. The 

 same thing occurs more distinctly in arteries, 

 and, whilst the rigor mortis remains in ac- 

 tivity, forms a powerful opponent to injections. 



III. GENERAL REMARKS WON VEINS 

 ORIGIN ; COURSE ; ANASTOMOSES ; PLEX- 

 USES, &c. General considerations of veins 

 arc to be made principally in relation to arte- 



* Kolliker and Sioliold's Zcitschrift. 1849. 



