RAPIDITY OF THE CIRCULATION. 107 



taken for granted ; and there are many facts which favor a contrary opinion. 

 It may be stated as a general rule, that when the acts of the heart increase in 

 frequency they diminish in force ; and this renders it probable that the ven- 

 tricle is most completely distended and emptied when its action is moderately 

 slow. When, however, the pulse is very much accelerated, the increased 

 number of pulsations of the heart might be sufficient to overbalance the 

 diminished force of each act and would thus actually increase the rapidity of 

 the circulation. In observations made on horses, by increasing the frequency 

 of the pulse, on the one hand, physiologically, by exercise, and on the other 

 hand, pathologically, by producing inflammatory action, it is shown that when 

 the pulse is accelerated in inflammation, the value of the contractions of the 

 heart, as represented by the quantity of blood discharged, bears an inverse 

 ratio to their number and is so much diminished as absolutely to produce a 

 current of less rapidity than normal. In the physiological increase in the 

 rate of the pulse by exercise, there was a considerable increase in the actual 

 rapidity of the circulation (Hering). 



With regard to the relations between the rapidity of the heart's action 

 and the general rapidity of the circulation, the following conclusions may be 

 given as the results of experimental inquiry : 



1. In physiological increase in the number of beats of the heart, as the 

 result of exercise, for example, the general circulation is somewhat increased 

 in rapidity, though not in proportion to the increase in the rapidity of the 

 pulse. 



2. In pathological increase in the rapidity of the heart's action, as in 

 febrile movement, the rapidity of the general circulation is generally dimin- 

 ished, it may be, to a very great extent. 



3. Whenever the number of beats of the heart is considerably increased 

 from any cause, the quantity of blood discharged at each ventricular systole 

 is very much diminished, either from lack of complete distention or from 

 imperfect emptying of the cavities. 



Phenomena in the Circulatory System after Death. Nearly every autopsy 

 shows that after death, the blood does not remain equally distributed in the 

 arteries, capillaries and veins. Influenced by gravitation, it accumulates in 

 and discolors the most dependent parts of the body. The arteries are always 

 found empty, and all the blood in the body accumulates in the venous system 

 and capillaries ; a fact which was observed by the ancients and gave rise to 

 the belief that the arteries were air-bearing tubes. This is readily explained 

 by the post-mortem contraction of the muscular coat of the arteries. If the 

 artery and vein of a limb be exposed in a living animal and all the other ves- 

 sels be tied, compression of the artery does not immediately arrest the current 

 in the vein, but the blood will continue to flow until the artery is entirely 

 emptied (Magendie). The artery, when relieved from the distending force 

 of the heart, reacts on its contents by virtue of its contractile coat and com- 

 pletely empties itself of blood. An action similar to this takes place through- 

 out the arterial system after death. The vessels react on their contents and 

 gradually force all the blood into and through the capillaries, which are very 



