122 



Prof. J. A. Mac William. On the 



[Oct. 24, 



and 60°, and the third during the period of cooling after the tem- 

 perature of 65° has been reached. These broad features in the 

 behaviour of the arterial strip are remarkably constant in their appear- 

 ance and behaviour, though there is much variation in detail. 



The extent of the first and second shortenings varies much in 

 different arteries and at different periods after death. Commonly 

 they show as quite large curves in the tracing, the shortening in each 

 case being followed by lengthening. The elongation f olio wing the first 

 shortening at 25 — 35° usually reaches its maximum at about 40° or a 

 little higher, when the temperature is steadily raised. Cooling down 

 to 35 — 25° does not restore the contraction seen at that phase when 

 the temperature was being raised; evidently the 25 — 35° contraction 

 is not a shortening conditioned simply by the presence of a tempera- 

 ture of 25 — 35°, but excited by a rise to that level. (Fig. 9.) 



When the artery has been kept some time longer (days) before 

 being heated, the contractions (a) at 25 — 35°, and (/3) about 47° 

 gradually become lessened and at a later phase disappear altogether ; 

 (P) persists longer than (a) in many arteries. (Figs. 7 and 11.) The 

 tendency to relaxation about 40° is often seen to outlast both the con- 

 traction curves (a) and (f3), though slight in amount compared to the 

 relaxation at 50—55°, into which it often grades. (Fig. 5.) 



(b) During the later stage (e.g., several days after death) the artery — 

 still more or less contracted — may show no very striking change till 

 a temperature of about 50° is reached, though there is often slight 

 relaxation beginning at about 40°. The usual 50 — 55° relaxation 

 leads to a complete abolition of such contraction as is present. 

 (Fig. 5.) 



When an artery from a recently-killed animal is placed and kept in 

 olive oil, the duration of its contraction is greatly prolonged, so that 

 very many days after death marked relaxation occurs when a trans- 

 verse strip is heated to 50 — 55°. As the contraction gradually 

 diminishes after a number of days, the amount of relaxation obtained 

 on heating lessens. 



In the carotid of the horse, distinct relaxation may occur at 50 — 55° 

 as long as 14 or even 18 days after death — though very much less 

 extensive than on earlier days, when more contraction was present in 

 the artery. 



Later, when contraction has quite gone, no sign of elongation is seen 

 at all on heating. 



Fig. 5 shows the relaxation that occurs in a transverse strip of 

 horse's cartoid kept in olive oil for 10 days p.m. The contraction 

 present in the early days had become greatly diminished by that time. 

 Fig. 6 shows that very slight but still appreciable relaxation occurred 

 18 days after death in the same artery; there had still been a very 

 small amount of contraction persisting. 



