198 



PLETHYSMOGRAPHY. 



pulse-beat, of course the water column in the manometer is raised. Fick placed a 

 float upon the surface of the water, and thus enabled the variations in the volume 

 of the fluid to be inscribed on a revolving cylinder. The curve obtained resem- 



Fig. 87. 



Mosso's Plethysmograph G, glass-vessel for holding a limb; F, flask for varying 

 the water-pressure in G; T, recording apparatus. 



bled the pulse-curve; it was even dicrotic. In Fig. 87 the movement of the 

 fluid is represented as conveyed to a Marey's tambour, T, similar to the recording 

 apparatus employed in Brondgeest's Pansphygmograph (p. 87). 



From the curve obtained we learn that (1.) The pulsatile variations 

 in the volume are similar to the pulse-curve. As the venous current is 

 regarded as uniform in the passive limb, every increase of the volume- 

 curve indicates a greater velocity of the arterial current towards the 

 periphery, and vice versa (Fick). (2.) The respiratory undulations 

 correspond to similar variations in the blood-pressure tracing 

 ( 85,/). Vigorous respiration and cessation of the respiration cause 

 a diminution of the volume. The limb swells during straining (v. 

 Basch) and coughing, and diminishes during sighing. (3.) Certain 

 periodic undulations occur, due to the regular periodic contractions 

 of the small arteries. (4.) Other undulations, due to various acci- 

 dental causes, affect the blood-pressure : changes of the position 

 of a limb acting hydrostatically, and dilatation or contraction of 

 the vessels in other vascular regions. (5.) Movement of the muscles 

 of the limb under observation causes diminution of volume (ex- 

 periment of Fr. Glisson, 1677); as the venous current is accelerated, 

 the musculature is also very slightly diminished in volume, even when 

 the mtra-muscular vessels are dilated. (6.) Mental exercise causes a 

 diminution in the volume of the limb, and so does sleep (Mosso). 

 Music influences the blood-pressure in dogs, the pressure rising or falling 

 under different conditions. The stimulation of the auditory nerve 

 is transmitted to the medulla oblongata, where it acts so as to cause 

 acceleration of the action of the heart (Dogiel). Compression of the 

 afferent artery causes a decrease, and compression of the vein an 

 increase in the volume pf tl^e limb (Mosso). 



