CAUSE OF THE EHYTHMICAL CONTRACTIONS OF THE HEART. 225 



changes of nutrition, by which, through the blood circulating 

 in its substance, the waste of its tissue is constantly supplied, 

 preserves the integrity of the fibres, and keeps them, conse- 

 quently, in a condition to contract. This is true, likewise, 

 of the ordinary striped muscular fibres. If the supply of 

 blood be cut off from the substance of the heart, especially in 

 the warm-blooded animals, the organ soon loses its irritabil- 

 ity. This was beautifully shown by the experiments of 

 Erichsen. This observer, after exposing the heart in a warm- 

 blooded animal and keeping up artificial respiration, ligated 

 the coronary arteries, thus cutting off the greatest part of the 

 supply of blood to the muscular fibres. He found, as the 

 mean of six experiments, that the heart ceased pulsating, 

 though artificial respiration was continued, in 23-J minutes. 

 After the pulsations had ceased, they could be restored by 

 removing the ligatures and allowing the blood to circulate 

 again in the substance of the heart. 1 The same is true of the 

 irritability of ordinary muscles, as has been lately shown by 

 the experiments of Dr. Brown-Sequard, though the continu- 

 ous action of the heart undoubtedly causes these phenomena 

 to be more marked and rapid. If we take a muscle which 

 has just lost its irritability and will no longer respond to the 

 most powerful stimulus, and inject fresh blood by the artery 

 supplying it, the irritability will be immediately restored. 3 



In the second place, the regular and powerful contraction, 

 of the heart is provided for by the circulation of the Hood 

 through its cavities. Though the heart, removed from the 

 body, will contract for a time without a stimulus, it can be 

 made to contract during the intervals of repose by an irri- 

 tant, such as the point of a needle, or a feeble current of gal- 

 vanism. For a certain time after the heart has ceased to 

 contract spontaneously, contractions may be induced in this 

 way. This can easily be demonstrated in the heart of any 



1 London Medical Gazette, July 8, 1842. 



3 BROWN-SEQUARD, Proprietes et Usages du sang rouge et du sang noir, 

 Journal de la Physiologie, 1858, tome i., p. 95 et seq. 

 15 



