1901.] Properties of the Arterial and Venous Walls. 



119 



different effects, according to the state of the artery at the time — 

 whether it is contracted or relaxed ; in the case of the contracted 

 artery there are also certain differences in its behaviour at the early 

 and the late stages of contraction. 



Relaxed Artery. — An artery in a state of relaxation behaves in essen- 

 tially the same way when heated, whether its relaxation is due to 

 (a) the gradual passing off of post-mortem contraction after some days, 

 or (b) to being kept at about body temperature for 24 hours, or (c) to 

 its having been frozen for some hours, or (d) to treatment with 

 potassium or ammonium sulphocyanide solution, or (e) exposure to 

 ammonia vapour. When the temperature is gradually raised there is 

 no important change, though slight shortening may gradually occur, 

 until it reaches 60 — 65° C, when a well-marked and commonly very 

 extensive contraction takes place ; this is seen whether a transverse or 

 a longitudinal strip is recorded, and the change is evident in an un- 

 opened segment of artery, suspended in the bath — the lumen becomes 

 very markedly diminished, while the arterial wall becomes much firmer 

 to the touch. When the shortening has been completed, and the tem- 

 perature is allowed to fall, there slowly occurs a certain amount of 

 lengthening, but this is always very incomplete. (Fig. 3.) 



FlG. 3. — Artery (ox) relaxed by freezing. Transverse strip, 10 mm. long; load, 

 2 grammes. The minor oscillations preceding the extensive descent of the 

 lever, beginning at 61°, are more distinct than usual ; they are often entirely 

 absent. Carotid (horse) relaxed by freezing. Transverse strip, 18 mm. long. 



This characteristic heat-contraction at 60 — 65° seems to be due to 

 the elastic and connective tissue elements of the artery, and not to 

 depend essentially on the properties of the muscular coat. For it is 

 well seen in pieces of artery which have had their muscle-proteids 

 almost completely extracted by prolonged maceration in large 

 quantities of saline fluids (ammonium chloride 13 per cent., &c). It 

 resembles the contraction got from a piece of tendon or of ligamentum 

 nuchse (ox), placed in the bath and recorded by the same apparatus. 



