The contrary opinion as to the existence of irritability in the arteries has been maintained by some of the most distinguished and accurate anatomists and physiologists, among whom are Hunter, Scemmerring, and Verschuir. It may be stated in a general manner, as an objection to the arguments of Bichat, founded on the circum stance of the arteries not having contracted when stimuli were applied to them in some experiments which he performed, that other irritable parts, even the muscles themselves, do not at all times contract on the application of stimuli. In fact, most of the experiments de tailed by Bichat, as proving the absence of irritability in arteries, have been performed by Hunter, Verschuir, and Hastings, and with results directly contrary to those obtained by that very distinguished anatomist. Verschuir found that the arteries contracted when stimu lated by the mineral acids, by electricity, and the application of the point of a scalpel. Dr. Thomson"' also saw them contract on the ap plication of ammonia, and when punctured with the point of a fine needle in the living body. Irritating the nerves by the galvanic fluid or bT caustic alkalies has been fol lowed by contraction of the arteries.f Mr. Iluntert found that the exposure of arteries to the air was followed by their contraction to such an extent as to produce their obliteration. An instance of this we have twice witnessed in the brachial artery when exposed during the progress of an operation for traumatic aneurism at the bend of the elbow. The contraction
of divided arteries is well known to be an efficient means of arresting haemorrhage, in op position to the force with which the blood is propelled through them by the heart's action.
In conclusion, we may observe that the arteries are proved to be both elastic and irritable ; that elasticity predominates in the large trunks, and irritability in the smaller branches ; diat their irritability, like that of muscles, is under the influence of the nervous system, and obeys the immediate application of chemical and mechanical stimuli, the effects of which must, however, be very much modified by the influence of the elasticity with which they are endowed. (See CIRCULATION.) In men the arteries are said to have their tunics thicker, and to possess greater density and a higher specific gravity than in women. The arteries are larger, more numerous,. and their coats are softer in young persons : they become more fragile, and their elasticity di minishes, in advanced life.
In the progressive development of parts the arteries appear before the heart; but in the chick, during its evolution, the veins of the yolk precede them in their development, as ascer tained by the researches of Malpighi,§ Haller,11 Wolff,1 Pander,*'' and Itolando.tt