. A text-book of physiology : for medical students and physicians . graph givesusually only the slow changes in volume of the arm, due to a greater or lessamount of blood. By using a more sensitive recorder and making the con- 606 CIRCULATION OF BLOOD AND LYMPH nections entirely rigid the smaller, quicker changes in volume caused by theheart beat are also recorded. A volume pulse is obtained resembling in itsgeneral form the pressure pulse given by the sphygmograph. When usedfor this purpose the instrument is described as a hydrosphygmograph. Records taken of the volume of the hand, foot, brai
. A text-book of physiology : for medical students and physicians . graph givesusually only the slow changes in volume of the arm, due to a greater or lessamount of blood. By using a more sensitive recorder and making the con- 606 CIRCULATION OF BLOOD AND LYMPH nections entirely rigid the smaller, quicker changes in volume caused by theheart beat are also recorded. A volume pulse is obtained resembling in itsgeneral form the pressure pulse given by the sphygmograph. When usedfor this purpose the instrument is described as a hydrosphygmograph. Records taken of the volume of the hand, foot, brain, or anyother organ show that in addition to the changes caused by theheart beat and by the respiratory movements, there are other moreirregular variations that are continually occurring, the cause of whichis to be found in the variations in the amount of blood in the and night these changes in volume take place, and they arereferable to the activity of the vasomotor system. Vasoconstrictionor vasodilatation in the organ itself cause what may be called. Fig. 250.—Detailed drawing of the glass plethysmograph with the arrangement of rub-ber glove to prevent leaking without compressing the veins. 2, The glove with its gauntletreflected over the end of the glass cylinder; 1 and 3, supporting pieces ot stout rubber tub-ing ; D and E, sections of outer and inner rings of hard rubber to fasten the reflected rubbertubing and reduce the opening for the arm. an active change in volume. But vasoconstriction or vasodilata-tion in other organs may cause a perceptible change, of a passivekind, in the volume of the organ under observation. For, sincethe amount of blood remains the same, a change in any one organmust affect more or less the volume—that is, the blood contents—of all other organs. General Distribution and Course of the VasoconstrictorNerve Fibers.—These fibers belong to the sympathetic autonomicsystem, and consist, therefore, of a preganglionic fiber arising i
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