THE CIRCULATION OF THE BLOOD AND LYMPH 117 



enclose the organ, the intervening space being filled up with liquid 

 (Fig. 47). The movements of the liquid are transmitted either 

 through a tube filled with air to a recording tambour, or directly to 

 a piston or float acting upon a writing lever. Special names have 

 been given to plethysmographs adapted to particular organs ; for 

 example, Roy's oncometer for the kidney. The method has been 

 successfully applied to the investigation of circulatory changes in 

 man, a finger, a hand or an entire limb being enclosed in the plethys- 

 mograph. With a fairly sensitive arrangement, every beat of the 

 heart is represented on the tracing by a primary elevation and a 

 dicrotic wave (Fig. 48). 



The general appearance of the curve is very similar to that of 

 an ordinary pulse-tracing, though there are some differences of 

 detail, especially in the time relations. A volume-pulse has 

 been actually observed not only in limbs and portions of limbs, 

 but also (in animals) in the spleen, kidney and brain, and other 

 organs, and in the orbit. 



The so-called cardio-pneumatic movements also constitute 



FIG. 47. PLETHYSMOGRAPH FOR ARM. 



F, float attached by A to a lever which records variations of level of the water in 

 B, and therefore variations in the volume of the arm in the glass vessel C. Or the 

 plethysmograph may be connected to a recording tambour. The tubulure at the 

 upper part of C is closed when the tracing is being taken. 



a volume-pulse, although of complex origin. This name is given 

 to the rhythmical changes of pressure accompanying the beat of 

 the heart, which can be detected in the air of the respiratory 

 passages when one nostril is connected with a recording tambour, 

 or water manometer, the other nostril and the mouth being closed, 

 and the respiration suspended in inspiration, with the glottis open. 

 Or the mouth may be connected with the recording apparatus, 

 the nostrils being closed. One factor in the production of these 

 movements may be the change of blood-volume in the soft 

 tissues of the mouth, naso-pharynx, and perhaps also in the 

 lower respiratory passages accompanying the heart-beat. Another 

 factor, and a more influential one, is the rhythmical alteration of 

 pressure caused directly by the alternate systole and diastole of 



