274 THE CIRCULATION. 



ments of the heart may be made to continue, in favorable cases, for 

 more than an hour ; and its actions may be studied by direct obser- 

 vation, li ke those of any external organ. 



The examination, however, requires to be conducted with certain 

 precautions, which are indispensable to success. When the heart 

 is first exposed, its movements are so complicated, and recur with 

 such rapidity, that it is difficult to distinguish them perfectly from 

 each other, and to avoid a certain degree of confusion. Singular 

 as it may seem, it is even difficult at first to determine what period 

 in the heart's pulsation corresponds to contraction, and what to 

 relaxation of the organ. We have even seen several medical men, 

 watching together the pulsations of the same heart, unable to agree 

 upon this point. It is very evident, indeed, that several English 

 and continental observers have mistaken, in their examinations, the 

 contraction for the relaxation, and the relaxation for the contrac- 

 tion. The first point, therefore, which it is necessary to decide, in 

 examining the successive movements of a cardiac pulsation, is the 

 following, viz : Which is the contraction and which the relaxation of 

 the ventricles ? The method which we have adopted is to pass a 

 small silver canula directly through the parietes of the left ven- 

 tricle into its cavity. The blood is then driven from the external 

 orifice of the canula in interrupted jets ; each jet indicating the 

 time at which the ventricle contracts upon its contents. The 

 canula is then withdrawn, and the different muscular layers of the 

 ventricular walls, crossing each other obliquely, close the opening, 

 so that there is little or no subsequent hemorrhage. 



When the successive actions of contraction and relaxation have 

 by this means been fairly recognized and distinguished from each 

 other, the cardiac pulsations are seen to be characterized by the 

 following phenomena. The changes in form and position of the 

 entire heart are mainly dependent on those of the ventricles, which 

 contract simultaneously with each other, and which constitute much 

 the largest portion of the entire mass of the organ. 



1. At the time of its contraction the heart hardens. This pheno- 

 menon is exceedingly well marked, and is easily appreciated by 

 placing the finger upon the ventricles, or by grasping them between 

 the finger and thumb. The muscular fibres become swollen and 

 indurated, and, if grasped by the hand, communicate the sensation 

 of a somewhat sudden and powerful shock. It is this forcible indu- 

 ration of the heart, at the time of contraction, which has been mis- 

 taken by some writers for an active dilatation, and described as 



