LV. STANNIUSS EXPERIMENT. 271 



(c.) Instead of applying No. 2 ligature, the ventricle may be cut 

 off from the auricles by means of a pair of scissors. Immediately 

 after it is amputated, the ventricle begins to beat. Stannius liga- 

 ture is of practical importance (i.) for arresting the uninjured 

 ventricle to measure its electro-motivity (Lesson XL VI.), (ii.) for 

 ascertaining the latent period of cardiac muscle (p. 272) (Hofmann, 

 " Function d. Scheidewandnerven d. Froschherzens," Pjiuger's 

 Archiv., Bd. 60, p. 139). 



2. Staircase Character of the Heart-Beats. 



Stannius a heart as above, i.e., arrest the beating of the auricles 

 and ventricle by tightening a ligature over the sino-auricular groove. 

 Attach the apex of the heart by means of a silk thread to a record- 

 ing lever, as in fig. 187, and record on a slow-moving drum. 



The heart is quiescent. Stimulate it with a single induction 

 shock at intervals of 5 seconds. Notice that the first beat is 

 lower than the second, the second than the third, so that each beat 

 exceeds its predecessor in amplitude until a maximum beat is 

 obtained. The amount of increase gradually decreases towards the 

 end of the series. This is the " Staircase " of Bowditch. 



3. Intracardiac Inhibitory Centre. 



(a.) Expose the heart in a pithed frog, tie a fine silk ligature 

 round the frsenum, and divide the latter between the ligatured 

 spot and the pericardium. Gently raise the whole heart upwards 

 to expose the somewhat whitish V-shaped "crescent " between the 

 sinus venosus and the right auricle. 



(b.) Arrange previously an induction coil for repeated shocks. 

 Place the electrodes which must be fine, and their points not too 

 far apart (2 millimetres) upon the crescent, and faradise it for a 

 second ; if the current be sufficiently strong, after a period of delay, 

 the auricles and ventricle cease to beat for a time, but they begin 

 to beat even in spite of continued stimulation. The electrodes are 

 conveniently supported on a short cylinder of lead. They can be 

 fixed to the lead by modeller's wax. 



(c.) Stimulate the auricles ; there is no inhibition or arrest. 



(d.) Apply a drop of sulphate of atropine solution (Lesson LVIL, 

 1) to the heart. Stimulation of the crescent no longer arrests the 

 heart. The atropine paralyses the inhibitory fibres of the vagus. 



4. Inhibitory (Crescent) Arrest Recorded. 



(a.) Take a tracing with Gaskell's lever. Stimulate the crescent 

 for 1-2 seconds with induction shocks as in 3, and observe the 

 arrest of the heart's beat (fig. 194). In the primary circuit place 



