270 PRACTICAL PHYSIOLOGY. [LV. 



6. Writing Point of Bayliss. — When it is necessary to diminish 

 friction as much as possible, this style is most excellent. Fix to a 

 straw a piece of gummed paper, and to this attach a bit of peritoneal 

 membrJine (same as is used for oncometers) and a bit of capillary 

 glass tube fused to a little ball at the end, and attached to the 

 peritoneal membrane by Front's glue. The membrane is made 

 broad to give rigidity in the direction of movement of the lever. 



7. Put a glass tube in the oesophagus and leave the heart attached. 

 Pass water at different temperatures through the tube and observe its effect 

 on the heart. 



(Engehnann, "Versuche am suspendirten HeTzen," Ffluger^s Archiv.^ liL 

 Ivi, lix. ; Kaiser, Zeits. f. Biol., xxxii., 1895.) 



LESSON LV. 



STANNIUS'S EXPERIMENT— INHIBITION— LATBNl 

 PERIOD OF HEART-MUSCLE, 



1. Stannius's Experiment.— Pith a frog, and expose its heart. 



(a.) With a seeker clear the two aortas from the auricles, and with 

 an aneurism needle pass a moist silk thread between the two aortas 

 and the superior venae cavae ; turn up the apex of the heart, divide 

 the frsenum, and raise the whole heart to expose its posterior 

 surface, and the crescent or Une of junction of the sinus venosus 

 and the right auricle. Bring the two ends of the ligature round 

 the heart — call this for convenience ISo. 1 Ugature — tie them, and 

 tighten the ligature just over the " crescent," so as to constrict the 

 line of junction of the sinus venosus with the right auricle. Befoie 

 tightening the ligature, observe that the heart is beating freely. 

 On tightening the ligature, the auricles and ventricle cease to beat, 

 and remain in a state of relaxation, while the sinus venosus con- 

 tinues to beat at the same rate as before. After a time, if left to 

 itself, the ventricle may begin to beat, but with an altered rhythm. 

 If the relaxed ventricle be pricked, it executes a single contraction, 

 i.e., a single stimulation produces a single contraction. 



{h.) When the heart is still relaxed, take a second hgature (Xo. 

 2), and preferably of a different colour, to distinguish it from No. 

 I ; place it round the heart, and tighten it over the an riculo- ven- 

 tricular groove, so as to separate the ventricle from the auricles. 

 Immediately the ventricle begins to beat again, while the auricles 

 remain relaxed or in diastole. 



