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.
Relaxed 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.
