For want of sufficient leisure, and convenient opportunities, I have neglected to make this experiment upon any animals of warm blood, except cats and rabbits. A few days after I had discovered the possibility of exciting the heart to contraction by means of zinc, and silver applied to its nerves, I procured an ordinary sized cat, and drowned it in water, as nearly as possible, of its own temperature. Four minutes after immersion, it was taken out of the water and dryed. Its thorax was immediately laid open, but no contractions were observed in any part of its heart, except in the right auricle, and even these were very slight. A plate of zinc was then placed in contact with the parvagum, and intercostal nerves, on one side of the trachea, and a half crown piece in contact with those of the other; both at the distance of about one third of an inch from the auricles. Every time the zinc and silver were brought into contact, complete contractions of the right auricle, and sometimes slight ones of the left were produced, but none in the ventricles. The contractions were observed to become stronger, in proportion as the metals were approached to the heart, and were strongest when one or both was in contact with the auricle. I think the contractions were fully as strong when molybdena, as when silver was used. No contractions could be excited, by arming any of the nerves of voluntary muscles, in this cat. The next experiment was made upon a female cat, far gone with young. She was drowned in very cold water, and although her thorax was opened the instant she had ceased to struggle, which was in less than four minutes after immersion, her heart had ceased to contract; nor could its contractions be renewed, either by the application of the metals in the way described, in the last experiment, or by pricking or otherwise irritating its surface: but the diaphragm, the intercostal muscles, the fore legs, and the ears, continued to contract long and vigorously, when the metals were as usual applied to their nerves. On cutting into the uterus, however, and taking out one of the young, I found both auricles and ventricles of its heart, contracting most vigorously, though the mother had now been dead upwards of twenty minutes.