1384 



VEIN. 



either side is the cardinal vein, and that the 

 heart is a muscular development on the coats 

 of that vessel. The action of this heart ap- 

 pears to be quite independent of the branchial 

 heart ; for, as Dr. Hall observes, " whilst the 

 latter beats sixty, the former beats one hun- 

 dred and sixty times in a minute. It con- 

 tinues for a very long time after the influence 

 of the pulmonic heart is entirely removed." * 

 I have never seen the action of the caudal 

 heart quite so rapid as is described by Dr. 

 Hall : in one individual, partly torpid from 

 cold, it contracted but sixty times in* the 

 minute ; but when this fish was warmed, the 

 number rose to one hundred and two, the 

 beats of the branchial heart being less than 

 half the caudal. 



The blood, which is deep red, appears to 

 flow into the extreme end of this organ in a 

 continuous stream, but is forced out at each 

 contraction from the other aperture in an 

 interrupted current. The absence of any re- 

 gurgitation, at the further end of the heart, 

 would suggest the presence of some valvular 

 apparatus there situate. The jet of blood, 

 sent forward at each contraction, may be 

 beautifully seen by holding up the tail of the 

 eel to the light ; it is seen as a regular, ar- 

 terial^ per-saltum, jet, passing along the vessel 

 in front of the heart, which, in the intervals 

 of each contraction, is empty: as Dr. Hall 

 expresses it, the blood is " propelled with 

 great velocity, at first with the appearance 

 of successive drops/' -j- This per saltum cur- 

 rent only exists a short distance, and gradu- 

 ally degenerates into a continuous, venous, 

 stream. When the parts are submitted to 

 low magnifying power, I have observed that 

 at each systole of the heart the veins at 

 the distal extremity of the organ are vio- 

 lently tugged in the longitudinal direction 

 (produced by the shortening of the heart in 

 its contracted state), and this exists as far as 

 several ramifications from the heart (d f d'). 

 A movement in the opposite direction takes 

 place at the diastole, which is doubtless as- 

 sisted by the elasticity of the vessels restoring 

 them to their former length. This circum- 

 stance, moreover, proves the complete con- 

 tinuity of structure of this organ with the 

 small vessels which furnish the blood upon 

 which it contracts. 



I have seen this best when the tail has 

 been cut from the body, the bloodless heart 

 still going on contracting. 



I have failed altogether to find any lym- 

 phatics going to this pulsating organ ; and the 

 facts which I have already adduced, that it 

 receives blood from behind, and transmits it 

 forwards ; the large aggregate quantity of fluid 

 which it propels in a given time ; the rhyth- 

 mical tension of the capillary veins, attached 

 to the distal end, at each contraction, as well 

 as the apparent absence of lymphatics, seem 

 to prove that it is a blood, and not a lymph, 

 heart. 



* Hall's Essay on the Circulation, p. 172. 

 t Loc, cit. 



II. PHYSICAL AND VITAL PROPERTIES. 

 As it regards the physical properties of veins, 

 it may be remarked that their walls are thin 

 as contrasted with arteries of the same calibre, 

 those of the upper extremity being less than 

 those of the lower; they are somewhat looser 

 in texture, especially externally, and more 

 extensile in the transverse direction are 

 distensible, and when distended they do not 

 readily return to their former dimensions ; 

 both circumstances being due, in a great 

 measure, to the general longitudinal diction 

 of their fibres : according to Soemmering 

 the resisting power of veins diminishes with 

 advancing age. 



The walls of veins are elastic, though less 

 so than arteries, which pre-eminently exhibit 

 that quality. 



The extreme thinness and slight physical 

 resistance of veins is the cause why they 

 collapse when empty. 



An empty vein presents very fine longi- 

 tudinal rugae on its inner surface. 



The tissue of veins is less distinctly yellow 

 than arteries, and frequently is stained of a 

 pinkish colour by the blood in contact with it. 



Though their physical properties are, for 

 the most part, of a negative character, they 

 nevertheless possess the property of tenacity 

 to a great degree, and are at least as strong as 

 arteries of the same capacity, though the 

 substance of the latter is so much more con- 

 siderable. 



Ligature applied to a vein produces a longi- 

 tudinal folding of the walls, which is very ap- 

 parent when the vessel is laid open after it 

 has been tied. An indentation is produced 

 across the inner surface of the vessel at the 

 line of ligature, caused by the complete or 

 partial rupture of its thin inner, longitudinal, 

 fibrous tunic. But the entire thickness of 

 the wall appears to have undergone a partial 

 cut, as though one element of the compound 

 mass of which it is composed had been divided 

 while the rest remained entire ; and it would 

 seem probable that a ligature applied tightly 

 around a vein would divide the crisp yellow 

 elastic tissue, while the tenacious white 

 fibrous element, with which it is mixed, 

 would remain entire. This probable expla- 

 nation I have found, upon microscopical ex- 

 amination, to be correct; the two parts, there- 

 fore, of a vein that has been ligatured, are 

 held together by the white fibrous tissue that 

 enters into the constitution of its walls.* 



Vital Properties of Veins. I am not aware 

 of any experiments which have been directed 

 to decide the amount of sensibility possessed 

 by .veins : it is probably, judging from anato- 

 mical grounds, exceedingly low. 



As regards vital contractility, it has been a 

 matter of dispute whether veins possess that 

 property or not. Soemmering held them to 

 possess it in an eminent degree, especially 

 under the influence of chemical stimuli, wh'lst 



* For some beautiful illustrations of ligatured 

 veins, I would refer to Cooper and Travers's Sur- 

 gical Essaj's, vol. i. plate 12. 



