LIGATURE AND SECTION OF THE HEART. 101 



than a or b separately. If the sinus venosus be separated it beats in virtue of a; 

 on the other hand, the heart rests because c is stronger than b. If the section be 

 made at the level of the auriculo-ventricular, the auricles stand still owing to c, 

 while the ventricle beats owing to 6. 



(2.) If the ventricle of a frog's heart be separated from the rest of 

 the heart by means of a LIGATURE, or by an INCISION carried through 

 it at the level of the auriculo-ventricular groove, the sinus and atria 

 pulsate undisturbed as before (Descartes, 1644), but the ventricle stands 

 still in diastole. Local stimulation of the ventricle causes a swrjh 

 contraction. If the incision be so made that the lower margin of the 

 auricular septum remains attached to the ventricle, the latter pulsates 

 (Rosenberger, 1850). 



(3.) Section of the Heart. Engelmann's recent experiments show 

 that if the ventricle of a frog's heart be cut up into two or more strips 

 in a zig-zag way, so that the individual parts still remain connected 

 with each other by muscular tissue, the strips still beat in a regularly 

 progressive, rhythmical manner, provided one strip is caused to con- 

 tract. The rapidity of the transmission is about 10 to 30 mm. per sec. 

 (Engelmann). Hence, it appears that the conducting paths for the 

 impulse causing the contraction are not nervous, but must be the 

 contractile mass itself. It has not been proved that nerve-fibres 

 proceed from the ganglia to all the muscles. 



[According to Marchand's experiments, it takes a very long time for the excite- 

 ment to pass from the auricles to the ventricle a much longer time, in fact, than 

 it would require to conduct the excitement through muscle so that it is probable 

 that the propagation of the impulse from the auricles to the ventricle is conducted 

 by nervous channels to the auriculo-ventricular nervous apparatus. In fact, in the 

 mammalian heart the muscular fibres of the auricles are quite distinct from those 

 of the ventricle.] 



(4.) It is usually stated that when the apex of a frog's heart is severed 

 from the rest of the heart, it no longer pulsates (Heidenhain, Goltz), but 

 such an apex, if stimulated mechanically, responds with a single con- 

 traction. 



Action of Fluids on the Heart. Haller was of opinion, that 

 the venous blood was the natural stimulus which caused the 

 heart to contract. That this is not so, is proved at once by the fact 

 that the heart beats rhythmically when it contains no blood. 



Blood and other fluids which are supplied to an excised heart are 

 not the cause of its rhythmical movements, but only the conditions on 

 which these movements depend. Thus, a heart which is too feeble to 

 contract may be made to do so by supplying it with a fluid containing 

 proteids, when a latent intra-cardiac mechanism is brought into action, 

 the albuminous or other fluid merely supplying the pabulum for the 

 excitable elements. 



