80 ELECTRO-PHYSIOLOGY CHAP. 



particular where it lasts for a considerable period, a more or less 

 extensive after-effect may regularly be observed the rhythmical 

 contractions even lasting for some time after tension is removed 

 from the heart. Ludwig and Luchsinger observed the same after- 

 effect on the frog's heart. 



In Helix pomatia it is easy to introduce a convenient canula 

 through the auricle into the upper part of the ventricle, and so 

 fill the heart with fluid (snail's blood). Under these conditions, 

 the internal pressure, together with the amount of wall-tension, 

 undergoes the simplest alteration. It is often sufficient to incline 

 the charged canula, with the heart, a little out of the horizontal, 

 apex downwards, in order to produce pulsations in the previously 

 quiescent ventricle. Another method, which is in many ways more 

 convenient, is to place the canula vertically with the heart, so that 

 the pressure of the entire column of fluid acts on the inner wall of 

 the ventricle. It is then easy by gradual immersion in a second 

 vessel, filled with 0*5 / salt solution, to raise the pressure acting 

 upon the external surface of the heart from zero to the point 

 at which internal and external pressure are equal, and wall-tension 

 therefore abolished. The difference of level of the fluid in the tube 

 and in the external vessels will then be the measure of amplitude of 

 wall-tension at any moment. The following figures illustrate the 

 changes of pulse-rate with change of wall-tension under the above 

 conditions : 



Height of Pressure. 



(Difference of Level in Canula Beats per minute. 



and External Vessel.) 



30 mm. 50 



15 ., 36 



8 21 



5 11 



2 



30 50 



Luchsinger (28) has also been able to show in the rabbit's 

 ureter the effect in this smooth, muscular organ, of wall-tension 

 on contraction phenomena ; so that in view of all the previous 

 evidence we cannot doubt that increased tension increases the 

 yield of work, not merely in striated skeletal muscle, but in an 

 even higher degree in the heart and smooth muscles. And this 

 increase is expressed not only in an increment of the individual 

 contractions, but also in the discharge or acceleration of rhythmic- 

 ally repeated contractions, i.e. the augmented (wall-) tension 



