192 CIRCULATION. 



" the heart is erected, and rises upwards to a point, so that at 

 this time it strikes against the breast and the pulse is felt ex- 

 ternally." * In the case of the son of the Yiscount Mont- 

 gomery, already referred to, Harvey gives a most graphic de- 

 scription of the manner in which the heart is " retracted and 

 withdrawn " during the diastole, and " emerged and protrud- 

 ed " during the systole. 



Succession of the Movements of the Heart. We have al- 

 ready followed, in a general way, the course of the blood 

 through the heart, and the successive action of the various 

 parts ; but we have yet to consider these points more in de 

 tail, and ascertain if possible the relative periods of activity 

 and repose in each portion of the organ. 



The great points in the succession of movements are read- 

 ily observed in the hearts of cold-blooded animals, where the 

 pulsations are very slow. In examining the heart of the frog, 

 turtle, or alligator, the alternations of repose and activity are 

 very strongly marked. During the intervals of contraction, 

 the whole heart is flaccid, and the ventricle is comparative- 

 ly pale ; we then see the auricles slowly filling with, blood ; 

 when they have become fully distended, they contract and 

 fill the ventricle, which in those animals is single ; the ven- 

 tricle immediately contracts, its action following upon the 

 contraction of the auricles as if it were propagated from 

 them. When the heart is filled with blood, it has a dark red 

 color, which contrasts strongly with its appearance after the 

 systole. This operation may occupy from ten to twenty sec- 

 onds, giving an abundance of time for observation. The 

 case is different, however, with the warm-blooded animals, in 

 which the anatomy of the heart is nearly the same as in man. 

 Here a normal revolution may occupy less than a second, and 

 it is evident that the varied phenomena we have just men- 

 tioned are followed with the utmost difficulty. In spite of 

 this rapidity of action, it can be seen that a rapid contraction 



1 Op. tit. 



