278 



PHYSIOLOGY 



CHAP. 



This experiment of Poiseuille was the starting-point for the 

 construction of the apparatus known as the plethysmograph, 

 because it serves to register the content, i.e. the variations in 

 volume, of any organ, owing to the dilatation and constriction of 

 the vessels it contains. It is easy to see that where the different 

 organs or parts of the body are highly vascular, the total 

 movements of passive or active dilatation or constriction of all 

 the arterial branches they contain must produce very consider- 

 able variations in volume. 



In order to estimate these variations in volume, Piegu (1846) 



introduced a limb into a vessel 

 tilled with lukewarm water and 

 closed completely, save at a 

 point through which passed the 

 vertical tube intended to show 

 the changes in volume. He 

 described the changes in volume 

 depending on cardiac, as well as 

 those depending on respiratory 

 rhythm. Chelius (1850), who 

 was not acquainted with the 

 previous investigations of Piegu, 

 investigated the changes in 

 volume of a limb by the same 

 method, and with the same 

 results. 



Ch. Buisson (1862), who dis- 

 covered the graphic method by 

 means of air transmission to a 

 writing tambour, subsequently 

 perfected by Marey, \vas the lirst 



Flo. 115.-Fran,ois -Frances plethysmograph, wh applied it to the plethySinO- 



for recording rapid changes of volume of graphs of PieSTll aild CliellUS. 



the hand, which are transmitted to a tarn- c * A T-,. -, /., o/r>\ -.i_i J.T 

 bour with highly sensitive lever. A. Tick (1868), With the Same 



object, connected the water-tight 



chamber in which the forearm was enclosed with a recording 

 water manometer, which directly recorded the pulsatile changes in 

 volume of the investigated limb upon a revolving cylinder. 



A. Mosso (1874-75) described another ingenious plethysmograph, 

 with which he intended to record in absolute values the changes 

 of volume in an isolated organ or a limb. Owing, however, to 

 the sluggishness with which the recording apparatus functions, 

 it is incapable of following the rapid passive changes due to the 

 cardiac rhythm, while it is able to record the slow changes in 

 volume due to the active contraction and dilatation of the vessels, 

 which are entirely independent of cardiac rhythm. We shall 

 return to this in Chapter X. 



