138 



Prof. J. A. Mac William. On the [Oct. 24, 



death is used, the series of increasing extensions is broken by a number 

 of smaller extensions to give place again to larger increments. This 

 is probably due to a contractile reaction of the muscular tissue of the 

 strip against the stretching force, or is a result of mechanical stimula- 

 tion caused by the clamps grasping each end of the strip. (Fig. 19.) 



Repeated Stretching. — When a transverse strip is weighted in the way 

 described and then unloaded, and after a time again weighted in the 

 same way, a second tracing is obtained differing very strikingly from 

 the first. It is in fact essentially similar to that obtained from a strip 

 of relaxed artery. The extension caused by the first weight is very 

 great. A third experiment of the same sort gives results essentially 

 similar to those of the second experiment. (Figs. 18 and 19.) 



Fig. 19. — Carotid (ox), contracted. Transverse strip. During the first loading 

 the largest extensions were followed by two or three small ones ; these were 

 succeeded by decidedly larger ones which gi'adually diminished in size. 



Longitudinal Strip of Contracted Artery. — With strips of similar dimen- 

 sions cut longitudinally from the arterial wail, the total elongation 

 produced by a total load similar to that used with transverse strips 

 (e.g., 240 — 340 grammes) is very much less than with transverse strips 

 — commonly between a half and a third. 



The character of the tracing differs in the two cases. In the longi- 

 tudinal strip there is only a slight increase, if any, in the amount of 

 elongation produced as the earlier weights are added, then a progres- 

 sive diminution. 



After unloading, the longitudinal strip recovers much more readily 

 and completely than the transverse strip ; the former shortens quite to 

 its original length. (Fig. 20.) 



Further, a repetition of the process of loading does not cause the 

 striking alteration in the tracing seen with the transverse strip • with 



