1890.] Papillary Muscles of the Heart. 81 



and though there is no stoppage in the act of contraction the rate 

 and extent of their contraction are in consequence diminished. 



The sudden powerful contraction of the musculi papillares is 

 followed by a stage in which the shortening of the muscles is 

 slowed and the ascent of the curve more gradual : and simul- 

 taneously there is a more rapid ascent of the heart-wall curve. 

 After this both portions of the ventricle remain for a comparatively 

 long period in a state of contraction unaccompanied by further 

 shortening, and the summits of both tracings are more or less 

 flattened. We then find that the papillary muscles begin to 

 expand before the rest of the ventricle. 



To sum up the above details : the papillary muscles begin to 

 contract later than the ventricular walls, and commence their 

 expansion at an earlier period. They act indeed only during that 

 period when upon a priori grounds we shoidd expect them to be 

 contracted, not pulling upon the segments of valve until these 

 have been brought into firm apposition by the increased blood 

 pressure, beginning to act also at a time when further increase 

 of pressure would tend to drive the segments upwards into the 

 auricle, and so cause regurgitation. Their contraction produces 

 a sudden definite increase in the intraventricular blood pressure, 

 well marked upon the blood pressure curves, and this increase 

 causes a diminution in the rate of shortening of the muscle of 

 the heart-wall, indicated by a depression upon the line of ascent 

 of the curve obtained from the ventricular wall. 



We hesitate to offer any explanation of this virtually inde- 

 pendent action of the papillary muscles : we can only declare that 

 the more we have studied the tracings obtained under various 

 conditions, the more we have been led to conclude that the 

 moment when they begin to contract is not primarily dependent 

 upon the moment of commencing ventricular contraction. We 

 find for example that an overdose of liquor strychnine may lead 

 to complete a synchronism between these two components of the 

 ventricular action ; or, again, there may be a ventricular systole 

 unaccompanied by papillary contraction, or vice versa. Again, the 

 first effect of strophanthus is to cause rapidly increasing force of 

 the contraction of the papillary muscles as compared with the 

 heart-wall. Further, the period of papillary contraction bears no 

 direct relation to the moment of origin of the pulse wave, to the 

 time that is when the blood begins to pour from the heart 

 into the arteries. Yet under normal conditions the pulse wave 

 would seem to begin almost at the moment when the musculi 

 papillares exert their first sharp strong pull upon the valves, and 

 so act as an additional factor in raising the intraventricular 

 pressure above that in the large arteries. In short, the phenomena 

 of the papillary contraction would appear to supply further proof 



