1878.] Mr. J. Priestley on Batrachian Lymph- Hearts. 139 



cation either of common non-polarizable electrodes or of electrodes of 

 platinnm wire. 



I. — Action of Induced Interrupted Currents. 



a. On the lymph- cardiac muscle detached from its nerve (as an ordinary 

 voluntary muscle maybe detached) by means of curare. — The electrodes 

 were laid on the back after the removal of the skin, as close to the 

 posterior lymph-hearts as possible. Under these circumstances the 

 lymph-hearts behave exactly like the surrounding striated muscles, not 

 differing from them to any remarkable extent, either in minimal sti- 

 mulus or in mode of contraction. 



b. On the lymph- cardiac spinal nerves after anatomical separation from 

 the lymph-cardiac spinal centre. — The spine and cord were snipped 

 through at the level of the 7th vertebra, and one non-polarisable elec- 

 trode was applied to the exposed lower end of the cord; while the 

 back of the 8th vertebral arch was removed, and the other electrode, 

 well moistened with normal saline solution, was introduced at the 

 window so made. Or a pair of platinum electrodes were slipped be- 

 neath the abdominal branch of the tenth spinal nerve running to one 

 of the posterior hearts, the heart having previously been brought to 

 rest by division of the same branch near the coccygeal foramen. Under 

 these circumstances the lymph-cardiac muscle-nerve preparation be- 

 haves like any ordinary muscle-nerve preparation, except that it pos- 

 sesses a much larger minimal stimulus. 



If contact between nerves and electrodes were not very perfect in the 

 spinal canal, or if currents near the minimal stimulating point were 

 employed, the usual firm tetanus of the lymph-hearts became broken 

 into a series of explosive, beat-like, or twitching movements. But, 

 under similar conditions, ordinary muscle-nerve preparations re-act in 

 a similar manner. 



c. On the lymph-cardiac spinal centre separated from the encephalic 

 inhibitory centre. — The frog was decapitated, and all the spinal nerves 

 were divided except the tenth. Windows were cut into the back of 

 the spinal canal, opposite the 5th and 8th vertebras, and into the 

 windows well-moistened non-polarizable electrodes were pushed. Or 

 the spinal canal was opened from the 5th to the 8th vertebras, and 

 platinum electrodes slipped beneath the cord or made to touch 

 the cord lightly one at each side at the level of the 6th vertebra. 

 Under these circumstances slight currents, strong enough to con- 

 tract at the same time the ilio-coccygeal muscles, slowed the 

 lymph-hearts ; stronger currents inhibited the hearts in diastole, and 

 still stronger currents caused a tetanic systole of the hearts like the 

 simultaneous tetanus induced in neighbouring nerve-supplied muscles. 

 The strong currents sufficient to cause in this manner prolonged 

 diastolic inhibition of lymph-hearts still dependent on their spinal 



