CHAPTER XXII 



EFFECT OF HYDROSTATIC PRESSURE, LOAD, AND LIGATURE 

 ON THE PULSATION OF DESMODIUM 



Effect of internal hydrostatic pressure on the pulsation of Desmodium — 

 — Expansive erection of leaflet under increased pressure : diminution 

 of the extent of systolic contraction — Effect of load : diminution of 

 period — Stannius' ligature on heart-beat — Parallel effect of ligature 

 on pulsation of Desmodium — Arrest of pulsation by a cut and revival 

 by electric shock. 



We have already seen that after the appHcation of a suitable 

 internal hydrostatic pressure the pulsation of the detached 

 leaflet of Desmodium becomes extremely regular. Some- 

 times a leaflet is found which has come to a state of standstill. 

 Internal hydrostatic pressure is often found in such cases to 

 renew the pulsatory activity. 



Effect of Hydrostatic Pressure 



The application of internal hydrostatic pressure enables 

 us, moreover, to understand the significance of the up-and- 

 down movements. Such movements may be the results 

 of contractions and expansions, as in a pulsating heart. In 

 the case of Desmodium we can induce expansion artificially 

 by internal hydrostatic pressure ; the shifting of the base- 

 line up or down will then distinguish for us the result of 

 expansion. Of the up-or-down movement again, the one 

 corresponding to expansion will be helped by increased 

 pressure ; the other, on the contrary, will be opposed. 



In subjecting the detached leaflet of Desmodium to 



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