brain;" and of "motor-impulses" being "conveyed to the muscles;" it is the stimulated nerves which excite the activity of brain and muscles, as the spark excites the explosive activity of gunpowder. We do not need three kinds of Contractility for flexors, extensors, and sphincters; nor do we need three kinds of Neurility for muscles, centres, and glands. One property serves for the three functions. The differences in the functions do not depend on the organs themselves, but on the connexion of these organs with others; the same organ (nerve) which, in connexion with a muscle, produces motion, in connexion with a gland would produce secretion.
The idea of different Neurilities must, therefore, be rejected. The two nerves having similar structure must have similar properties; but these properties may be put to different uses. My critic in the British and Foreign Medical Review seems to have wholly misunderstood me; and thinks that had I been "longer engaged in the study of physiology," I should be "less inclined to rest upon an apparent similarity of structure as justifying an inference of identity of property." Perhaps his longer study will enable him to enlighten me on this point; at present my conviction is, that if the similarity were only apparent, it would amply justify the inference; whereas, if the similarity were real, and not apparent only, it would carry a demonstration. My critic seems to think otherwise; and he is kind enough to say that my "dogmatism on this point, indeed, is absolutely confounding to those who have been accustomed to look with marvel at the diversity of operations performed by elementary parts which present no appreciable structural differences." One naturally feels a little perplexed at having confounded others by one's dogmatism, when the point in question is so excessively simple as the discrimination between properties and uses. I would, therefore, submit that the operations performed by means of chain cables, tenpenny nails, marling spikes, and grappling irons, though various enough, are not generally held as evidence that the iron of which they are all composed has different properties in each. I never denied that different nerves had different functions, but only that they had different properties. If any one conceives that the anterior roots send forth nerves having a Neurility as widely opposed to that of the nerves issuing from the posterior roots as Motion is to Sensation, let his evidence be produced. If he conceives that the anterior nerves will only act in one direction, and the posterior in another and contrary direction, so that the motor nerve cannot excite a centre, and the sensory cannot excite a muscle or a gland, let him produce his evidence. Meanwhile, I will suggest the evidence against such a notion.
It has been proved by Schiff, and others, that the nerve will conduct both ways; not only will it conduct electricity, it will conduct its own proper stimulus. In other words, it has been shown experimentally that Neurility will act both in the centripetal and centrifugal directions. I will now call attention to a still more striking fact, one which has strangely enough been overlooked, probably because investigators were seeking only the phenomena of sensation and motion; a fact which dis-
