( 385 ) 



Nvall ;iii(l the (liircrciiccs will (l('|»('ii<l upon llic siiontaiicons or ihc 

 exlru (•(uilruclioii Ixmiiu' llic uiosl coiisidcraltlc. 



TIk' (jiicslioii iiiiisl lio\\r\('i- now lx» pnt : w liv does a coinplch» 

 conipcnsalorv pansc alwavs (or alniosl alwavs, h]N(;i;i,MANN "i follow 

 llie exii-a systole of llic anriclc in llic anipliihian licarl and w li\ in 

 llie mamiiialiaii heart only under certain conditions r 



Tiie answer may rnn as follows: In (Mpially Unilt np parts of {\\c 

 heart muscle the stimulus is also eipially conducted to all sides, Imt 

 where hu' w halexcr reason the state ol the muscle fibres is not 

 everywhere the same, the cojiduclion of the stimulus will neither lie 

 the same. 'Idiis is the reason that the conduction of the stimulus of the 

 aiirich> on the xciitricle, in u'eneral of one di\ision of the heart on 

 the other, takes place much slower than inside the wall of ani'icle 

 or venli-icle. When ccmdnction takes |»lace i]i the direction opposed 

 to the normal, this distinction \\ill not make itself less felt. And 

 Just as the slower conduction may he the cause that e\tra-s\ stoles 

 of the venti-icle never recede (piickly eiionuh to have a disturhinü' 

 elfecl on the rhythm of the lireat veins, the diirerenlialion hetwceii 

 \eins, sinns and ventricle in the frog's heart will he the cause, that 

 here a stimulation of the auricle is not (jinckly enough conducted 

 lhron<iii the transition places to disturU the rhythm at the venae 

 caxae. Moreoxer this |>ossil)ilily seems so nnich the slighter, Itecaiise 

 in the fro^-'s heart muscle fibres with a slronu' aiitojnalic irritability 

 ascend hiuh np in the vena cava and so caiuiot be readied so easi I \- 

 by an extra stinudns. As this differentiation of the cardiac muscle 

 i)etween vena cava and a1ri(»-ventricnlar limit is missinu' \\)v the 

 nuimnuils, it is no wondei' that the dislurbinu' inflnence on the foi-- 

 niation of the stimulus at the vena ca\a occurs just in tlnMnammalian 

 iiearl. 



If finally this explanation is the i-iulil one, the place where the 

 anricle of the mannnaiiaii hearth is stinuilated, will liaxc its c\\'or\ 

 on llie len,i;th of the comj)ensatory pause: perha|»s it will be ])()ssibl(> 

 to estal)lish for ]iot too small hearts an<l where the conduction 

 of the nuiscle has already somewhat slackened, that for anriculai- 

 stimidalion far from the \ena ca\a the compensatory |)anse is 

 longer or even complete, whilst the pause becomes shoi'lei' accordinu" 

 to tlie anricnlar stimulation takin.ii' place closer to the \ena ca\a. 

 For snch an experiment the stimulation would always have to be 

 ellectcMl exactly in the same moment of the heart period, excry time 

 eqnally long after the pi-eceding systole. 



