THE HEART 55 



further support of this view Kaiser claims to have shown that, 

 after extirpation of Bidder's ganglia, this second ligature no longer 

 has any effect in starting the ventricle. Now a stimulus applied 

 is followed by only one contraction instead of by a series of con- 

 tractions. We shall refer to this experiment again later on. 



Kronecker and Schmey claim that when a needle is thrust into 

 a certain spot in the dog's ventricle, the heart immediately falls 

 into fibrillary contractions as far as the ventricles are concerned. 

 The needle is thrust into the ventricular septum at the lower end 

 of the upper third. The experiment frequently fails. It is 

 adduced, however, by its authors as evidence of the neurogenic 

 theory. 



The experiments of Carlson upon the heart of a horse-shoe crab 

 (Limulus) undoubtedly afford evidence of neurogenic origin of a 

 heart beat. The heart in this case consists of a tube 10 to 15 cm. 

 long, divided into segments by the origin of arteries. During 

 systole all the parts appear to contract simultaneously, although 

 it is probable that there is really a rapid wave of contraction. 

 Three nervous strands (one median and two la'teral) run along 

 the heart and anastomose freely. The median contains ganglion 

 cells, and one especially large ganglion. This strand can be easily 

 separated from the heart without injuring the latter. Fine 

 branches pass into the muscle substance. Carlson has shown that 

 if the whole of this median nerve be removed, the heart imme- 

 diately ceases to pulsate ; if a part only be removed, then activity 

 ceases in the corresponding portion of the heart. The ganglionated 

 chain therefore appears to be the site of origin of the excitatory 

 wave in this heart. 



As regards the conduction of the impulse the neurogenic theory 

 holds that it is conducted by nerves. The delay in the passage 

 from auricle to ventricle is said to arise in Bidder's ganglia. 



The chief points in the evidence brought forward for nervous 

 conduction are 



(1) The assertion by Kronecker that he has produced allo- 

 rhythmia (inco-ordination of auricle and ventricle) by cutting a 

 nerve running between auricle and ventricle. 



(2) At first the fact that in the mammalian heart no muscular 

 connection was known to exist between auricle and ventricle. For 

 instance, MacWilliam, as the result of his researches, came to the 

 conclusion that in the mammalian heart, at any rate, the mode 



