400 THE MECHANICS OF THE CIRCULATION, HEMODYNAMICS 



exposed to the medium directly, as in Mosso's instrument, 1 or may first be 

 surrounded by an envelope of soft rubber (Fig. 210). The changes in volume which 

 the organ undergoes may be recorded by means of an ordinary U-shaped [manom- 

 eter filled with water, or with the help of tambours of the type designed by Marey 

 and Hiirthle, and the piston-recorders constructed in accordance with the suggestions 

 of Roy, 2 Ellis, 3 Schafer, 4 Hiirthle, 5 and Lombard. 6 A very convenient and prac- 

 tical recorder has been described by Brodie, 7 the essential constituent of which is 

 a pair of bellows made of thinnest rubber and equipped with a delicate writing 

 lever. A plethysmograph, which is frequently made use of in the laboratory, is the 

 one designed for the reception of the hand and forearm (Figs. 213and214). Itcon- 

 sists of a cylindrical chamber of glass which is filled with warm water through two 

 openings in its upper wall. The space around the arm is made air-tight by a cuff of 



FIG. 214. DETAILED DRAWING OF THE GLASS PLETHYSMOGRAPH WITH RUBBER GLOVE TO 



PREVENT ESCAPE OF WATER. 



2, The glove with its gauntlet reflected over the end of the glass cylinder; 1 and 3, 

 supporting pieces of stout rubber tubing; D and E, sections of outer and inner rings of 

 hard rubber to fasten the reflected rubber tubing and reduce the opening for the arm. 

 (Howell.) 



rubber membrane which is adjusted in such a way that it does not compress the 

 blood-vessels of this locality. The small orifice in the far end of this cylinder is 

 connected with the recording instrument. This arrangement allows any change 

 in the volume of the arm to cause a corresponding displacement of the water which 

 in turn varies the level of the recording lever. 



The uses to which this instrument may be put are very manifold. It has been 

 stated above that the cardiometer may be employed to determine the volume 

 of the output of the heart by obtaining the differences in the volume-curve of this 

 organ during systole and diastole. In a similar way the attempt has been made by 

 Brodie to measure the blood supply of the kidney by temporarily blocking its 

 venous return and recording the increase in volume occurring at this time. The 



1 Diagnostik des Pulses, Leipzig, 1879. 



2 Jour, of Physiol., iii, 1880, 203. 



3 Ibid., vii, 1886, 309. 



4 Ibid., xx, 1896, 1. 



5 Pfluger's Archiv, liii, 1893. 



6 Am. Jour, of Physiol., iii, 1890. 



T Jour, of Physiol., xxvii, 1902. A very simple method of registration has been 

 described by O. Miiller (Archiv fur Anat. und Physiol., 1904, Suppl.). 



