268 



PRACTICAL PHYSIOLOGY. 



[liv. 



a Gaskell's clamp (fig. 191, C), fixed in an adjustable arm attached 

 to the same stand. To support the upper lever, fix to it a fine 

 thread of caoutchouc (E), and attach the latter to a slit or other 

 arrangement on the top of the support. The clamp consists of two 



fine narrow strips of brass, 

 like the points of a fine pair 

 of forceps, which can be 

 approximated by means of a 

 screw. 



(b.) Expose the heart of a 

 pithed frog. Tie a fine silk 

 thread to the apex of the 

 ventricle, and another to the 

 upper part of the auricles, and 

 excise the heart. Tie the 

 auricular thread to the upper 

 lever and the ventricular one 

 at a suitable distance to the 

 lower lever. 



(r,) Adjust the clamp (fig. 

 191, C) so as to clamp the 

 heart in the auriculo- ventricu- 

 lar groove, but at first take care not to tighten it too much, or 

 merely just as much as will support the heart in position. After 

 fixing the heart by means of the clamp, fix the two levers so 

 that both are horizontal, and adjust the caoutchouc thread attached 



FlO. 19T.— Gaskell's Clamp. C Heart in clamp ; 

 A. Auricular, and V. Ventricular lever; i'. 

 Elastic to raise A after it is pulled down. 



FlO. 192.— Tracing from Auricle (^1) and Ventricle (F) by Oaskell's Method. 

 T. Time in seconds. 



to the upper one, so that it just supports the upper lever, and when 

 its elasticity is called into play by the contracting auricles pulling 

 down the lever, it will, when the auricles relax, raise it to the 

 horizontal position again. 



(d,) Adjust a time-marker to write exactly under the writing 



