477 



The nutritive relations of the muscular tissue and the blood are suf- 

 ficient for the maintenance of mere motility, but they are not suffi- 

 cient for the maintenance of rhythmic motion ; they can maintain the 

 power of acting upon external stimulus, but cannot give spontaneity 

 of action, or regulate the time or manner of acting. 



It is interesting to observe in these experiments three different 

 modes of action of the heart : (1) the truly rhythmic, in which the 

 contractions of its several parts, or of some of them when separated, 

 ensue spontaneously (i, e. without evident stimulus or change of ex- 

 ternal conditions), and observe a definite order and proportion of 

 time ; (2) such as may be excited by stimulus, which, beginning at 

 the cavity stimulated (whichever it may be), are effected simultane- 

 ously, or with a scarcely appreciable difference of time, by all parts 

 of the walls of that cavity ; then follow, with a certain interval, in 

 the other cavities ; and then are not repeated in the same order, but 

 give place to the true rhythmic action, which they may for once 

 have prevented or inverted; (3) those which ensue on stimulus, 

 when the heart or any of its parts is utterly exhausted, and which 

 commence at the point stimulated, and thence slowly travel once to 

 all other points connected with it by continuity of muscle. 



Now, of these three modes of action, the last may be ascribed to 

 mere motility, such as the intestines and the stomach have, and 

 such as is maintained by the nutritive relations of the muscular sub- 

 stance and the blood in its vessels. The second may be due to the 

 same, acting with more energy ; or it may be ascribed, as by Bidder * 

 and Rosenbergerf, to the action of reflecting nervous centres in the 

 ganglia of the heart. But what of the third, the rhythmic, which every 

 experiment shows to be essentially different from both of these ? 



It is explicable, and all the experiments are consistent, on the 

 belief (which many before me have entertained) that it depends on 

 certain nervous centres in the nerve-ganglia of the heart ; which cen- 

 tres, byspontaneous discharges of nerve-force, cause the muscular struc- 

 tures to contract. These centres (rhythmic centres as they have been 

 called) being injured or hindered in their operation, the rhythm ceases, 

 though the motor power is not lost ; or these centres, being cut 

 away with certain portions of the heart, the other portions cease to 



* Muller's Archiv,' 1852, p. 163. 



f De centris motuum cordis. Dorpat, 8vo, 1850. 



2 N 2 



