CIRCULATION. 409 



side, and not through an exaggerated lessening of the latter and an actual 

 increase of the former. In this case, too, the base would tend to become 

 more circular during the systole by means of a less marked change from the 

 diastolic form. 1 



It has been said that in systole the ventricles are somewhat shortened 

 in the exposed heart, and probably also in the unopened human chest. In 

 the open chest the apex does not recede at all in virtue of this shorten- 

 ing; on the contrary, the base of the ventricles is seen to move toward 

 the apex, and away, therefore, from the spine. Experiment has proven that 

 the foregoing is true also of the unopened chest. 2 It has been noted already 

 that this movement of the base, which in the upright chest would be a descent, 

 is accompanied by a lengthening of the aorta and pulmonary artery as their 

 distention takes place. Very probably it is the thrust of the lengthened arte- 

 ries which largely causes the descent of the base of the contracting ventricles, 

 which descent compensates for the shortening of the ventricles and retains the 

 apex in contact with the chest-wall. 



The Impulse or Apex-beat. It must always have been a matter of com- 

 mon knowledge that, in man, a portion of the heart lies so close to the chest- 

 wall that, at each beat, the soft parts of that wall may be seen aud felt to pul- 

 sat over a limited area. This is commonly in the fourth or fifth intercostal 

 space, midway between the left margin of the sternum and a vertical line let 

 fall from the left nipple. A similar pulsation may be observed in other mam- 

 mals. The protrusion of the chest-wall at the site of this " impulse " or " apex- 

 beat " occurs when the arteries expand, and the up-stroke of their pulse is felt ; 

 and the recession of the chest coincides with the shrinking of the arteries away 

 from the finger. The impulse proper, that is the protrusion of the chest-wall, 

 occurs, therefore, at the time of the systole of the ventricles. By far the most 

 important factor of the apex-beat is probably the effort of the hardening ven- 

 tricles to change the direction of their long axis against the resistance of the 

 chest-wall. A heart severed from the body and bloodless, if laid upon a 

 table, lifts its apex as it hardens in systole and assumes its proper form. If a 

 finger be placed near enough to the rising apex to be struck by it, the same 

 sensation is received as from the impulse. 



It is interesting to note that around the point where the soft parts of the 

 chest are protruded by the impulse, they are found to be very slightly drawn 

 in at the time of its occurrence. This drawing-in is called the "negative 

 impulse," and must be caused by the diminution in size of the contracting 

 ventricles. These are air-tight within the chest, and so their forcibly lessened 

 surface must be followed down, in varying degrees, under the pressure of 

 the atmosphere, by the elastic and yielding lungs and by the far less yield- 

 ing soft parts of the chest-wall. 



The apex-beat can be brought to bear in various ways upon a recording 

 lever, and thus be made to inscribe upon the kymograph a rhythmically fluc- 

 tuating trace, which is called a cardiogram. Considerable attention has been 



1 J. B. Haycraft : loc. tit. J Haycraft : loc. eit. 



