1010 PHYSIOLOGY 



weight of moving parts, so as to possess small inertia and be capable of 

 registering a rapid rise of pressure without entering into oscillations of 

 its own. Several methods have been adopted for this purpose. In one 

 (Chauveau and Marey) a cardiac ' sound ' (Fig. 390) is passed down the 



FIG. 390. Diagram of Marey's cardiac ' sound,' consisting of a long tube 

 ab, terminating at one end in the ampulla m, which is covered with 

 an elastic membrane. The side-piece c serves to indicate the position 

 of the ampulla after it has been introduced into the vessels. 



jugular vein into the right auricle or ventricle, or down the carotid 

 artery into the left ventricle. The cardiac sound is a stiff tube having 

 an elastic bulb or ampulla at the end which is to be inserted into the 

 heart. The bulb is supported by a steel frame, so that it is not com- 



FIG. 391. Marey's tambour. 



a, axis of lever ; 6, metal tray covered with rubber membrane, and com- 

 municating by tube / with free end of cardiac sound 



pletely compressible by external pressure. The free end of the tube is 

 connected with a writing tambour (Fig. 391), a small round metal tray 

 covered with a delicate elastic membrane. To the top of the membrane 

 a lever is attached by which any change of pressure on the ampulla may 

 be recorded on a moving smoked surface. The large size of these 

 sounds makes it difficult to use them on any animal smaller than the 



FIG. 392. Diagram to show construction of Hiirthle's membrane manometer. 



ass or horse. In smaller animals, such as the dog, the question has 

 been investigated by the use of a manometer such as that of Hiirthle. 

 In this instrument (Fig. 392) the changes of pressure are recorded by the 

 oscillations of a thick rubber membrane which covers a very small tam- 

 bour. The tambour is filled with magnesium sulphate solution, which is 

 also used to fill the tube connecting with the heart. This tube can be 



