IQ2 



THE CIRCULATION OF THE BLOOD 



of the cavities of the heart, the movements of the piston are recorded by means 

 of the lever, C. Attached to the lever is a section of a pulley, H, the axis of which 

 coincides with that of the steel ribbon, ; while, firmly fixed to the piston, is 

 the curved steel piston rod, /, from the top of which a strong silk thread, J, 

 passes downward into the groove on the pulley. 



This thread, /, after being twisted several times around a small pin at the 

 side of the lever, enters the groove in the pulley from above downward, and 

 then passes to be fixed to the lower part of the curve on the piston rod as shown in 

 the smaller figure. 



The movement of the lever, C, is controlled by the resistance to torsion of 

 the steel ribbon, E, to the middle of which one end of the lever is securely fixed 

 by a light screw clamp, F. At some distance from this clamp, the distance 

 varying with the degree of resistance which it is desired to give to the move- 

 ments of the lever, are two holders, G t G r , which securely clamp the steel 

 ribbon. 



As the torsion of a steel wire or strip follows Hooke's law, the torsion being 

 proportional to the twisting force, the movements of the lever point are pro- 

 portional to the force employed to twist the steel strip of ribbon in other 

 words, to the pressures which act on the piston, B. To make it possible to 

 record satisfactorily the very varying ventricular and auricular pressures, the 

 resistance to torsion of a steel ribbon adapts itself very conveniently. 



This resistance can be varied in two ways, ist, by using one or more pieces 

 of steel ribbon or by using strips of different thicknesses; or ad, by varying 

 the distance between the holders, G, G', and the central part of the steel 

 ribbon to which the lever is attached. 



FIG. 166. Hiirthle's Spring Manometer. A , Viewed from the side; B, viewed from the top. 



Rolleston's conclusions are: That there is no distinct and separate 

 auricular contraction marked in the pressure curves obtained from the right 

 or the left ventricle, the auricular and ventricular rises of pressure being 

 merged into one continuous rise. He concludes that the tricuspid and 

 mitral valves are closed before there is any great rise of pressure within the ven- 

 tricle above that which results from the auricular systole, a, figure 165. The 



