274 CIRCULATION OF THE BLOOD. 



contraction, but on the interval of relaxation which separates 

 one systole from its successor. (See fig. 235.) 



Chauveau found the systolic pressure in the horse to be about 

 128 millimetres in the left ventricle, and 25 millimetres in the 

 right. These numbers express the relative, values of the me- 

 chanical work done by the two ventricles. The absolute values, 

 as has been already stated, are unknown, from the impossibility 

 of determining the quantity of blood which flows through the 

 heart in a given time. 



SECTION VII. INTRINSIC NERVOUS SYSTEM OF THE HEART. 



Nothing is as yet known either as to the anatomical distribu- 

 tion of nervous elements in the hearts of mammalia, or as to 

 the functions which they perform. In the frog, both have 

 been the subject of minute and repeated investigation. We 

 have already had frequent occasion to observe that the frog's 

 heart continues to beat after its removal from the body, and 

 that this rhythmical movement often goes on for hours or even 

 for days, under favorable circumstances. From this it is evi- 

 dent that its maintenance is dependent on conditions which are 

 contained within the heart itself. 



68. Proof that the Ganglion Cells contained in the 

 Heart are the Springs of its Automatic Movement. 

 It is objected by some physiologists that the rhythmical con- 

 tractions go on not merely in the whole heart when deprived 

 of blood and severed from the cercbro-spinal nervous system, 

 but also in mere fragments of the muscular substance which 

 cannot be admitted to contain ganglion cells. The answer lies 

 in the results of the following experiments: 



The heart of a frog just removed from the body is placed in 

 a watch-glass containing serum, or three-fourths- per cent, saline 

 solution, in which it will continue to pulsate for many hours. 

 Small portions of muscularsubstance are then taken either from 

 the s/m/s IVWJSMS, the auricles, or the ventricle, and observed 

 in a drop or two of the indifferent liquid, under a low r power. 

 It is then seen that portions taken from the sinus, the auricles, 

 or that part of the ventricle which is in the immediate neighbor- 

 hood of the auriculo-ventricular constriction, pulsate rhythmi- 

 cally, but that similar portions taken from the ventricle near 

 the apex do not pulsate. The pulsating bits ma}' be further 

 divided with sharp scissors under the dissecting microscope, 

 until preparations are obtained which consist of only a few 

 muscular fibres. Many of these still contract rhythmically, 

 each fibre becoming shorter and thicker at each contraction, but 

 not losing its rectilinear contour. If now the pulsating and 

 non-pulsating shreds are submitted to microscopical examina- 

 tion, it will be found that, whereas ganglion cells cannot be 



