LABORATORY MANUAL OF PHYSIOLOGY. 



For this determination a larger vascular area is required. An 

 instrument used for determining volume changes is called a ple- 

 thysmo graph. One of the simplest devices is that of Porter. 



This consists of a glass tube, with a rubber collar made to fit 

 snugly around the middle finger. The tube is connected with a 

 recording tambour, and the volume changes of the finger are re- 

 corded upon a slowly revolving drum. 



These changes are rhythmical in character and correspond to 

 the rhythm of the heart-beat. In addition, larger waves may be 

 written as a result of general or local vasomotor changes. 



A larger record is obtained through the use of Mosso's water 

 plethysmograph, by which the volume changes of the forearm are 

 recorded. 



This consists of a large glass cylinder provided with four open- 

 ings one for the insertion of the forearm, one for connection with 

 the recording apparatus, one for filling the system with water, and 

 one for the insertion of a thermometer. 



A simple recording device is the water pen of Kronecker. This 

 is a small box connected by rubber tubing with the plethysmo- 

 graph cylinder upon the surface of the water in which a cork sheet, 

 supporting a writing lever, is floated. 



The hand and forearm are anointed with vaseline, a rubber col- 

 lar is fitted snugly just below the elbow, the hand and forearm are 

 inserted in the cylinder, and the rubber collar fitted about the 

 flange of the opening through which the arm is inserted. The cyl- 

 inder is connected with the recording apparatus, the cylinder and 

 recording apparatus are filled with water, the thermometer is in- 

 serted in the opening provided for it, the filling bottle is clamped 

 off, and the recording pen is applied to the surface of a slowly re- 

 volving drum. 



Set up the apparatus as described above and take a normal- vol- 

 ume pulse tracing. 



While the tracing is being recorded, elevate the free hand and 

 arm above the head. Is there any change in volume of the arm in 

 the cylinder? 



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