CIRCULATION OF THE BLOOD. 541 



small automatic nervous centres situated in the walls of the heart was 

 first pointed out by Remak. These cardiac ganglia are three in number 

 and are of different functions ; two are motor ganglia, one an inhibitory 

 ganglion. The motor ganglia are the ganglia of Remak, situated at the 

 opening of the inferior vena cava; the ganglion of Bidder is situated in 

 the left auriculo-ventricular septum. These ganglia are entirely independ- 

 ent of the will, and, under the excitation of the temperature and chemical 

 composition of the blood, communicate to the muscular fibres of the 

 heart their motor impulse. The inhibitory ganglion is that of Ludwig, 

 situated in the inter-auricular septum. The function of this ganglion is 

 to regulate the transmission of motor impulses, produced by the motor 

 ganglia, to the fibres of the heart. It fulfills this end, however, not by 

 acting directly on the muscular structure of the heart, but through the 

 mediation of the motor ganglia ; by this means it compels the motor 

 ganglia to dispense the power which they develop during excitation 

 rhythmically and moderately. As regards the manner in which these 

 ganglia produce the rhythmical contraction of the heart, little is known, 

 but that they are the prime factors in producing the rhythm of the car- 

 diac revolutions, with its various modifications, is capable of experimental 

 demonstration. 



If the heart be removed from a frog and placed in a watch-glass 

 containing a dilute saline solution, it will be seen that it still continues 

 to pulsate in as exact rhythm and as vigorously as when in its normal 

 condition. Under favorable circumstances it might be kept pulsating 

 for many hours. This is not, however, the case with the frog alone ; the 

 heart of almost any cold-blooded animal will beat outside of the body, 

 and a similar observation has even been made on the heart of man. But, 

 to return to the share of the motor ganglia in producing cardiac pulsa- 

 tion : As before stated, one motor ganglion is situated at the opening of 

 the inferior vena cava, and the other in the auriculo-ventricular septum. 

 If the apex of the ventricle be cut off from the base of the heart with a 

 pair of sharp scissors, dividing the ventricle at about its lower third, 

 instantly the apex ceases to pulsate, while the remainder of the heart 

 still goes on contracting as before. The apex has been cut off from its 

 motor ganglia. It may be said that the section of the heart has destroyed 

 the irritability of the muscular fibres of the apex, but if the apex be 

 irritated with a weak induction current it responds ; it will again pulsate, 

 to again, however, become quiescent on removal of the irritation. It 

 has, however, been stated by Meruncowicz that the apex fragment will 

 again commence to pulsate if kept supplied with defibrinated blood or 

 artificial serum ; so, also, after an hour or more the apex will usually 

 again spontaneous^ commence to pulsate. 



Further, if in a narcotized frog the ventricle is compressed trans- 



