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THE CIRCULATION OF THE BLOOD AND LYMPH 



This may be readily recorded by means of a pie thysmo graph, an 

 instrument consisting essentially of a chamber with rigid walls which 

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

 (Fig. 56). 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 plethysmo graph. With a fairly 

 sensitive arrangement, every beat of the heart is represented on the 

 tracing by a primary elevation and a dicrotic wave (Fig. 57). 



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 ob- 

 served not only in limbs and por- 

 tions of limbs, but also (in animals) 

 in the spleen, kidney and brain 

 and other organs, and in the orbit. 



Fig. 56. Plethysmograph (MosSty. M, balanced test-tube, in communication with 

 the glass vessel, D, which contains the arm, escape of water being prevented by 

 the rubber cuff, A. When water passes from vessel D to M, or from M to D, 

 M moves down or up, and its movements are recorded by the writing-point N. 

 M is steadied by the liquid in P, into which it dips. 



The so-called cardio-pneumatic movements also constitute 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 



