. A text-book of human physiology . ries caused by increasinginternal pressures, which is a matter of much greater importance for under-standing the circulation, the results of investigators differ widely. WhileMarey and others have found that the cubic enlargement runs the samecourse as the elongation of the strip cut from the wall, Eoy asserts that thisis the case only in arteries taken from animals and men who have sufferedfrom some wasting disease, and finds that with perfectly sound arteries theincrease in volume with equal increments of internal pressure rises at firstup to a certain lim
. A text-book of human physiology . ries caused by increasinginternal pressures, which is a matter of much greater importance for under-standing the circulation, the results of investigators differ widely. WhileMarey and others have found that the cubic enlargement runs the samecourse as the elongation of the strip cut from the wall, Eoy asserts that thisis the case only in arteries taken from animals and men who have sufferedfrom some wasting disease, and finds that with perfectly sound arteries theincrease in volume with equal increments of internal pressure rises at firstup to a certain limit (variously given for the dog from 32 to 120 mm. Hg.).but with still higher internal pressure the distensibility falls (Fig. 75). At any rate, it is certain that the cubic enlargement of the arteries beyondthat given by a certain internal pressure, Mhich as a rule is not higher thana medium, normal blood pressure, becomes less and less with equal incre-ments of pressure. From which it follows that when the arterial blood pressure. Fig. 75.—The cubic enlargement of the aorta of a rabbit, untler a uniformly increasing internal pressure, after Roy. is already high, any steady increase in the quantity of blood discharge fromthe heart will cause a more than proportionate rise in the blood pressure andwill correspondingly increase the work of the heart. From results thus far at hand it appears that with any given increase inpressure the arteries are distended relatively more the farther they are situ-ated from the heart. In the body arteries as well as veins are always on the stretch long:itudiiially,whatever the internal pressure; for the moment they are cut out of the body theyat once retract, becoming: shorter and thicker. It is always possible to iind astretching: force which will give an exseeted vessel the dimensions it would haveif it were completely fixed in sifu, when empty. This stretching force expressedas pressure in millimeters of Ilg is looked upon by R. Fuchs as th
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