SECTION IX 



FUNCTIONAL PECULIARITIES OF THE CARDIAC 

 MUSCLE TISSUE 



CHAPTER XXVIII 

 THE ORIGIN OF THE HEART BEAT 



The Excised Heart. — If the heart of a cold-blooded animal is re- 

 moved from the body and is placed in a nutritive medium under proper 

 conditions of moisture and temperature, it will continue to beat 

 rhythmically for many hours, and even for days. Essentially the same 

 result may be obtained with the hearts of warm-blooded animals, but 

 inasmuch as their storative power is slight, they require a constant 

 supply of nutritive material. Thus, it will be found that the mamma- 

 lian heart ceases to beat very soon after the circulation has been inter- 

 rupted, but may be made to resume its activity later on by perfusing 

 it through its coronary blood-vessels. This procedure consists in 

 connecting the aorta with a pressure reservoir containing an 0.8 

 per cent, solution of sodium chlorid. Ringer's fluid, or defibrinated 

 blood through which bubbles of oxygen are passed at a constant rate. 

 Under the most favorable conditions an excised heart may be kept 

 beating rhythmically for many hours ; moreover, if it is merely intended 

 to incite the contractions without having them continue for any length 

 of time, it is sufficient to use oil or paraffin in place of the nutritive 

 fluids just mentioned. Evidently, the mechanical stimulus derived 

 from the distention of the coronary vessels suffices to activate the 

 musculature and to keep it in this condition for a moderately long 

 time. These experiments may be repeated with smaller segments of 

 the heart as well as with narrow strips of the ventricles. In the latter 

 case, it is sufficient to immerse them in solutions of certain inorganic 

 salts. Larger pieces of the ventricles may be made to beat rhythmi- 

 cally by perfusing them through their supply channel. 



The conclusion to be drawn from experiments of this kind is that 

 the power of rhythmic contraction is inherent in the hearts of all 

 vertebrates.^ Their connection with the central nervous system, there- 

 fore, is not essential to their activity and merely serves the purpose of 

 bringing them into functional relation with the other organs and tissues. 



It has previously been shown that various conditions may arise in 



1 First taught by Haller in 1757. 

 331 



