140 Mr. J. Priestley on Batrachian Lymph-Hearts. [Feb. 28, 



centres, are also of a strength to cause powerful tetanns of the same 

 lymph-hearts when applied to their nerves in the spinal canal, as des- 

 cribed under b. 



It should be noticed that the same explosive, pulse-like movements 

 occurred here as under b, when the conditions were similar. 



This action of the interrupted induced current on the lymph- cardiac 

 spinal centres is not abolished by the local or systemic exhibition of 

 solutions of atropia. 



II. Action of Constant Currents. 



The currents were applied to the structures tested by means of 

 non-polarizable electrodes of ordinary form. 



a. On the lymph-hearts brought to rest by separation from their spinal 

 centres. — After operations involving extensive bleeding, separation 

 from their spinal centres is, in nearly all cases, followed by permanent 

 stand-still of the dependent hearts. In the experiments described the 

 frogs were decapitated and eviscerated, all the spinal nerves except 

 the tenth were divided, and the thighs amputated in order to obviate 

 any disturbing muscular movements. The electrodes were applied to 

 the base of the back near the heart to be examined, sometimes in a 

 direction laterally across the heart, and sometimes in the longitudinal 

 axis of the heart ; or the heart was carefully excised with its surround- 

 ing connective tissue, placed upon the clay of one electrode, and 

 lightly touched with the point of the other. In the latter way of 

 experimenting no attention was paid to the relation of the current to 

 the axes of the heart, on account of the small size of the organ in 

 R. temporaria. Under these circumstances with various strengths of 

 battery from 2-3 small Daniell's cells to 16-18 Grove's, nothing but 

 ordinary opening and closing contractions could be caused. 



b. On the lymph-hearts still beating in normal dependence on their 

 spinal centres. — The electrodes were placed either on the lateral or the 

 longitudinal axes of the hearts, as in a. Under these circumstances, 

 in whatever direction the current flows, the pulsation of the hearts is 

 hampered or inhibited, the hampering affecting rather the depth than 

 ♦the frequency of the beats. 



c. On the lymph-cardiac spinal centres. — The well-softened electrodes 

 were pushed in at windows opening into the spinal canal through the 

 5th and 7th or 8th vertebral arches, after the frog had been decapitated 

 and the spinal nerves, except the tenth, all divided ; or one electrode 

 was placed on the upper end of the cord exposed in decapitation, while 

 the other was placed in the window through the lower vertebral arch. 



a. On the acting spinal centre. — Different results were obtained accord- 

 ing to the direction and strength of the current, varying from complete 

 stand- still in diastole to pulsation much more rapid than normal ; but 

 all seem capable of explanation by the aid of the known laws of 



