The next experiments related to the effects upon the heart of cer- 

 tain stimuli applied to the brain or spinal marrow. Spirit of wine, 

 applied to the brain or to the upper portions of the spinal marrow, 

 excited considerable increase of the heart's action, but not when ap- 

 plied to the lumbar portion. A watery solution of opium or infusion 

 of tobacco also, occasioned a slight increase ; but this was soon suc- 

 ceeded by more languid action of the heart, which, however, reco- 

 vered its power as soon as these applications were washed off from 

 the brain or spinal marrow. 



When tincture of opium is applied to the hind legs of a frog, the 

 animal is deprived of sensibility in less than a minute ; but this effect 

 was found not to arise from the opium, but solely from the spirit of 

 wine in which it is dissolved, which alone has the same effect, while 

 a watery solution of opium has no such power. But though a frog 

 be rendered insensible by application of spirit of wine to its feet, the 

 heart nevertheless continues to act, and its force is even increased 

 by subsequent application of spirit of wine to the brain or spinal 

 marrow. 



The effects of opium or tobacco were also found to be the same 

 upon frogs as they had been observed in former trials upon rabbits. 



In the course of these experiments it was observed, that consider- 

 able pressure either on the brain or spinal marrow, had little or no 

 effect on the motions of the heart ; and it was further remarked, that 

 the peristaltic motion of the intestines was not affected thereby, and 

 indeed that it in general obeyed the same laws as those of the heart 

 in regard to being influenced by stimuli applied to the brain or spinal 

 marrow, but at the same time that it is not dependent on those parts 

 for their continuance. 



Since the apparent inconsistency between two facts, both well as- 

 certained, evidently arises from some imperfection of our knowledge 

 of the principles by which they are to be explained, the author en- 

 deavours to elucidate this subject by further experiments. 



By applying strong stimuli, and repeating them, to the spinal mar- 

 row of a frog, the muscles were made to contract till their irritability 

 was exhausted. In a second frog the nerves supplying the muscles 

 of one leg were divided, and the irritability of its muscles was ex- 

 hausted by the application of salt to the muscles themselves ; and 

 afterwards that of the other leg was exhausted by the same means, 

 without dividing the nerves. Under these different circumstances 

 the irritability was sooner exhausted in that limb to which the nerves 

 remained entire. It appeared therefore, that the property of the 

 heart, of being excitable independent of nervous influence, is common 

 to it with other muscles ; and also its property of being excited 

 through the medium of its nerves, although it possesses the latter in 

 a much less degree, being sparingly supplied with nerves, because its 

 usual stimulus is immediately applied to itself, while that of the vo- 

 luntary muscles is conveyed to them from the sensorium. 



And it further appears to the author, that, in the same manner, the 

 spinal marrow is capable of performing its functions independently 



