4 CONTRACTILE TISSUE OF ARTERIES. 



it what is termed, xantho-proteinic acid, which, with ammonia, produces a 

 yellow xantho-proteinate of ammonia. On applying this test, with the 

 requisite cautions, to the coats of blood-vessels, Dr. Bonders found that 

 the middle arterial coat alone assumed the characteristic yellow colour. 

 The other coats, as well as all the coats of veins, remained unchanged in 

 colour. 



But the most satisfactory evidence is that furnished by some recent 

 experiments of Ed. and E. H. Weber,* in which they applied the stimulus 

 of electro-magnetism to small arteries. One principal circumstance which 

 induced Professor Miiller to deny the muscularity of arteries, was the 

 inability of himself, and of other experimenters who had occupied them- 

 selves on the subject, to produce the slightest movements in arteries by 

 means of galvanic and electric stimuli, while in all true muscular tissues 

 these stimuli give rise to manifest contractions. An explanation of the 

 failure of these physiologists, may be found in the circumstance that in 

 nearly all their experiments, the arteries examined were of large size, 

 such as the aorta and the carotids, in which the thickness of the muscular 

 coat is comparatively small. The experiments of the Webers were, on the 

 other hand, performed on the small mesenteric arteries of frogs ; and the 

 most striking results were obtained, when the diameter of the vessels 

 examined did not exceed from I to I of a Paris line. When a vessel of 

 this size was exposed to the electric stream, its diameter, in from five 

 to ten seconds, became one-third less, and the area of its section about 

 one-half. On continuing the stimulus, the narrowing gradually increased, 

 until the calibre of the tube became from three to six times smaller 

 than it was at first, so that only a single row of blood-corpuscles 

 could pass along it at once ; and eventually the vessel became com- 

 pletely closed and the current of blood arrested. When the experi- 

 ment was so conducted, that only a limited part of an artery was exposed 

 to the electric stream, the extent of tube involved in the contraction was 

 equally limited, not exceeding from I of a line to a line. The contraction 

 did not ensue the moment the irritation was applied, and it continued for a 

 short time after its withdrawal. The walls of the artery were rendered 

 somewhat thicker at the contracted part, but the narrowing of the canal 

 was proportionally greater than the increase in thickness acquired by the 

 walls. Previous to the complete closure of the artery, the velocity of 

 the stream of blood passing through it, in accordance with hydraulic prin- 

 ciples, became considerably accelerated. When an artery was irritated 

 only for a short time, or by a feeble galvanic current, it speedily resumed 

 its former calibre on the stimulus being withdrawn, and again contracted 

 on a re-application of it; but when the irritation was long continued, or 

 the stream very powerful, the portion of the artery narrowed by it lost 

 the power of again contracting, and even dilated, until it became double 



* Mullet's Archiv. 1047, p. 232, et seq. 



