144 Prof. J. A. Mae William. On the [Oct. 24, 



Pressure was then lowered to 0. An hour later the artery had not 

 yet diminished to its original volume — the oil was 28 mm. from the 

 starting-point. 



Pressure again raised. 



Pressure.— 20 40 60 80 100 120 140 160 180 200. 

 Expansion.— 18 14 12 10 6*5 7 4-5 4*5 3-5 4-5. 



Carotid (Ox) relaxed by keeping it in blood at 39° C. for 24 hours. Lumen 

 6 mm. Length of artery used 16 mm. 



Pressure raised as before. 



Pressure. — 



20 



40 



60 



80 



100 



120 



140 



160 





180 



200 



220 



240 



260 



280 



300. 





Expansion. — 



14 



11 



10 



10 



10 



10 



9 



8 



10 



10 



8 



9 



8 



6 



6. 





Pressure lowered to 0. 



An hour and three-quarters later oil was 20 mm. from starting- 

 point. 



Pressure again raised. 



Pressure.— 20 40 60 80 100 120 140 160 180 200. 

 Expansion.— 27 211611 7 6 6 5 3 4. 



Carotid (Ox) relaxed by Ammonia Vapour. — A strongly-contracted 

 artery exposed to ammonia vapour changed as follows : — Length 

 diminished from 28 to 24 mm. ; lumen enlarged from 2 mm. to 

 5 — 6 mm.; wall thinned from 2 mm. to about 1 mm. Length of 

 artery used in plethysmograph, 13 mm. 



Pressure.— 20 40 60 80 100 120 140 160. 



Expansion. — 129 6 5 5 5 4 4. 



Contracted Artery. — When a portion of artery is excised from a 

 recently killed animal and prepared for experiment upon its distensi- 

 bility in the way described above, it is usually in a state of pretty 

 strong contraction, the contraction present on excision being as a rule 

 markedly augmented by the necessary manipulation, tying in the cannula 

 and wooden plug, &c. When the internal pressure is raised step by 

 step by equal increments (e.g., of 20 mm. Hg.), the artery at first yields 

 relatively little and the augmentation of its volume is slight. Suc- 

 cessive rises of pressure cause increasing amounts of expansion, and 

 in the case of a thick-walled and strongly-contracted artery (e.g., 

 carotid of ox) the increasing expansion may go on up to very high 



