118 



Prof. J. A. MacWilliam, On the [Oct. 24, 



heating was varied within pretty wide limits and the temperature was. 

 often kept steady at various levels for considerable periods. 



In many experiments the oil bath was not heated directly by th& 

 lamp ; it was immersed in an outer beaker of water, which was placed 

 on a piece of gauze and heated in the way mentioned. In most cases- 

 two strips were heated simultaneously in the bath, and made to record 

 on the same drum. The temperature was determined by a thermo- 

 meter fixed in the oil-bath with the bulb close to the arterial strips. 

 A time record usually showing periods of 5 minutes was simultaneously 

 inscribed. Shortening of the arterial strips is indicated by a downward 

 movement of its lever. The magnification was generally three times. 



In many experiments the recording lever was directed at right angles 

 to the circumference of the drum, so that its point moved in a straight 

 line perpendicular to the direction of movement of the recording surface 

 — not in an arc of a circle like a lever used in the ordinary way. 

 Ordinates were drawn through the marks in the time tracing ; at one- 

 end of each ordinate the exact time was inscribed, at the other end the 

 temperature at that moment. 



Instead of spiral springs small weights (e.g., 1 — 2 grammes) wer& 

 sometimes employed to maintain tension of the arterial strip during 

 the experiment. 



Slight contraction may occur before the heating has begun, and 

 shortly after the strip has been suspended — probably due to the- 

 mechanical stimulus supplied by compression of each end of the strip 

 by the clamp which holds it, perhaps assisted by the slight tension of 

 the strip when connected with the recording lever. 



Poisseuille* stated long ago that the force of reaction excited by dis- 

 tension of an artery was greater than the force used to distend it.: 

 And Baylissf has recently described a number of experiments upon the 

 reaction of intact arteries (isolated from the central nervous system) to* 

 the distending force of a raised blood pressure. 



Frequently pieces of excised artery (unopened) J 2 — 3 cm. long were 

 suspended in the bath alongside the arterial strips, and examined from 

 time to time, so as to correlate the changes seen in the unopened tube- 

 with those shown graphically by the transverse or longitudinal strips, 

 The results obtained by these two methods were entirely concordant^ 

 Experiments were made on arteries with strong muscular coats like the 

 carotid, and also on the aorta and pulmonary artery. 



Experiments on the Carotid Artery. — Heating an artery produces very 



* ' Journal de Physiologie,' par M. Majendie, vol. 8, p. 272. See note in John 

 Hunter's 'Works' (London, 1837), vol. 3, p. 157. 



f 'Journal of Physiology,' vol. 26, " Proceedings of Physiological Society," 

 p. 29. 



% This means excised segments of artery not laid open longitudinally, though, 

 open at the ends. 



