On the Properties of the Arterial and Venous Walls. 191 



absent, there is only the 60 65 shortening with the usual lengthen- 

 ing on cooling. Tracings are given to illustrate these changes. The 

 general behaviour of the arterial muscle is strikingly similar in its 

 general character to what occurs in the bladder (cat), while its muscle 

 is unquestionably alive. 



The changes seen in strips from the aorta and the pulmonary artery 

 are slighter in amount (though similar in general character) in accord- 

 ance with the relatively small amount of muscular tissue in the walls 

 of those vessels. 



The effects of heat upon saline extracts of contracted and relaxed 

 arteries are examined and compared with the changes shown by the 

 arterial strips. It is shown that there is no necessary relation between 

 the phases of shortening and the coagulation of proteids in the arterial 

 wall. Coagulation occurs in an acidulated 5 per cent. MgS0 4 extract 

 of artery at 45 50 and at 55 60. Experiments were made to- 

 ascertain whether proteid coagulation occurred in the tissues of the 

 arterial wall at the same temperatures as in saline extracts. 



Contraction v. Rigor Mortis. 1'ost-mortciu contraction is evidently a 

 true persistent contraction very different in its character from the 

 rigor morii* of skeletal muscle. This is shown by evidence of various 

 kinds (1) the effects of stimulation; (2) sulphocyanide ; (3) heat; 



(4) the results of extension of strips of the arterial wall by weights ; 



(5) the behaviour of the artery when distended by internal pres- 

 sure, &c. 



Elasticity of the Arterial and I'enous Walls. This was tested by 

 weighting strips cut transversely and longitudinally from the carotid, 

 &c. Relaxed arteries, as well as veins, gave maximum elongation with 

 the first addition of weight, while contracted arteries showed incre- 

 ments of length increasing up to a maximum and then declining, the 

 curve being first convex towards the axis and then concave in 

 marked contrast to what is obtained with skeletal muscle and other 

 tissues. AVhen stretched a second time the maximal elongation comes- 

 at the beginning. 



Strips from the aorta and pulmonary artery behave much like strip* 

 from a relaxed carotid. 



Both the relaxed and contracted arteries show increased extensibility 

 with light weights when stretched a second time. 



Illustrative tracings are given in the paper. 



Relation of Cubic Capacity to Internal Pressure. The portion of artery 

 examined was placed in an oil plethysmograph, and the air pressure in 

 the interior of the artery was raised by means of a system of pressure 

 bottles. 



Kelaxed arteries were found to be most distensible at low pressures ; 

 the maximum increase of volume per unit rise of pressure comes when 

 the pressure is raised from zero, as a rule. 



