24 



This instrument consists of two essential parts. The first is a 

 kind of flat tripod which rests upon the wall of the thorax over 

 the heart, and is fastened by a band passing round the body. 

 Between these three feet is a drum with an india-rubber mem- 

 brane, which is actuated by a knob which can be made by 

 properly adjusting the height and position of the tripod to lie 

 upon the fifth intercostal space just over the heart's apex. The 

 interior of the drum is connected with a long caoutchouc tube, 

 by means of which it communicates with the second part of the 

 apparatus. 



This consists of a drum, smaller than the one just mentioned, 

 with a stem, by which it can be held in a support. It has an 

 india-rubber membrane, to which is* fixed a lever, the end of 

 which bears a point for writing on a revolving drum. The 

 effect of this arrangement is that the motions of the heart 

 produce changes of pressure in the tube, and these again are 

 translated into movements of the lever and recorded upon the 

 surface of the drum. 



97. Sphygmograph, devised by Marey, for the demon- 

 stration of pulse movements. 



Lent by the Biological Laboratory, Royal College of 

 Science. 1878. 



The instrument is fastened around the wrist so that the end 

 of a spring lever rests upon the radial artery and shares its 

 pulsations. The movements of this spring are magnified by 

 another light lever, which carries at its extremity a sharp 

 tracing point. This point writes upon a blackened strip of 

 paper, which is carried forwards by clockwork as the lever 

 moves up and down. 



98. Drawings of the Pletismograph, devised by Dr. A. 

 Mosso, of Turin, for exhibiting the variations in volume 

 in separate organs or individual limbs. 



Given by Dr. A. Mosso. 1877. 



The organ (usually a liver or kidney of some small animal) 

 is immersed in a closed vessel full of oil and its vessels supplied 

 with defibrinated blood at a pressure which can be determined 

 by the experimenter. With the vessel of oil is connected a tube, 

 through which any excess due to the expansion of the organ 

 passes out and falls into a counterpoised vessel connected with 

 a pen, which writes on a revolving drum. Thus the changes in 

 the volume of the organ are registered. In the case of the 

 changes in the volume of a limb being measured it is passed 

 into the open end of a tube and made water-tight by a band of 

 caoutchouc. The rest of the apparatus is arranged on the same 

 principle as before. 



