The heart, according to Volkmann, is more flabby after death than it is during life : the intestines, in like manlier, are collapsed in the dead body, and appear like so many flat tened bands ; while in the living body, at least in small animals, they present more the aspect of tubes; the looseness of the skin and of the scrotum in the dead body is also remarkable, compared with the appearance they' present in the living. These differences depend upon a loss of tone. The tone of the involuntary or organic contractile structures „does not, however, depend on the brain or spinal cord, inasmuch as it does not cease after these parts have been destroyed, but may continue in the aniphibia at least for months thereafter. It depends, according to Volkmann, upon the sympathetic ; and from this he derives another argument in favour of the view that the ac tivity of the sympathetic or ganglionic nerve fibres does not depend upon the brain or spinal cord. After division of a motor nerve, the muscles immediately became relaxed, which shows, according to him, 1st, that the tone depends on an active contraction of the muscle ; 2nd, that the mere irritability of the muscle is not alone sufficient for the restoration of this contraction, but also requires an ex citing cause or motor impulse ; 3rd, that the nerve conveys this motor impulse to the muscle; 4th, that the place where this motor impulse arises or originates is not the nerve itself, but is a central organ. If now, after destruction of the brain and spinal cord, the tone in the organic muscles and many other contractile tissues continues, it follows from this that, besides the brain and spinal cord there rnust still be another centre from which motor impulses proceed, and this can only be the ganglia of the sympathetic.
In reaard to this question, so far as our knowledbge of the anatomical constitution of the sympathetic extends, the most probable view would seem to be that it is partly inde pendent, in its action, of the brain and spinal cord, partly dependent. The circumstance that there are present in its branches nume rous nerve-fibres which are derived from the brain and spinal cord, would appear to indicate that the organs to which such fibres proceed must be to a certain extent influenced by the central masses of the nervous system. From the circumstance, however, that it probably contains:other nerve-fibres which do not arise in the brain and spinal cord, and more particu larly from the circumstance of gray nervous matter being present in different parts of its extent, it seems not unreasonable to suppose that the influence which it exercises over the parts towhich it is distributed originates, partly at least, not in the brain or spinal cord, but in the gray or ganglionic matter mentioned. If we attribute to the gray matter of the brain or spinal cord a certain property of originating nervous force, it seems unreasonable to deny similar properties to the gray rnatter occurring in other parts of the nervous system. What
ever properties are possessed by the one, analogous properties are, it is to be expected, possessed by the other. Besides, no other hypothesis which has been proposed to ac count for the function of the ganglia appears to harmonise so closely with known facts as that which regards them as so many distinct peripherical nervous masses endowed with properties similar to those which are com monly attributed to a nervous centre.
Properties of fibres of sympathetic. Sensory properties.— In regard to the sensory pro perties of the sympathetic, different statements are made by authors. Bichat, Magendie, Dupuy,* and others, observed that section of the branches of the sympathetic was attended with few or no signs of pain. Dupuy states that he has removed the superior cervical from the horse without the operation appear ing to call forth any marked expression of pain. Section of the sympathetic cord in the neck may often be performed in the rabbit without any indication of sensibility being given. Haller found, on the other hand, that irritation of the hepatic plexus in the dog gave rise to distinct signs of pain ; the same results were also obtained by Meyer from irritation of the solar plexus. When he made incisions into the superior cervical ganglion, he found, contrary to what had been observed by Dupuy, that clear indications of pain were elicited. From ligature applied to the renal nerves, as well as frorn the application of chemical or mechanical stimuli to the semilunar ganglia, animals suffered great pain. So, also, Flourens* found that on irritating ,the semi lunar ganglion in dogs the animals exhibited distinct signs of pain, and the same results were obtained by Brachet t, from irritation of the thoracic ganglia. Frequently, according to Brachet, stimuli, when first applied to a part of the nerve, do not give rise to pain ; after wards, however, when the part has been ex posed to the air for some minutes, if irritation be now applied distinct signs of pain are elicited. Longet I, in like manner, found that on irritation of the semilunar ganglia the animal almost invariably exhibited indications of more or less pain being vroduced. In other animals, where the lunnbar ganglia were sub jected to experiment, he found, like Brachet, that it was only after prolonged irritation that signs of pain were evinced. So, also, accord ing to Valentin§, when the cavities of the thorax or abdomen are opened as quickly as possible, and pressure applied to the semi lunar ganglion, to the splanchnics, or to any other branch of the sympathetic, sometimes no signs indicative of sensibility are evinced. When, however, they have been exposed to the air for a short time they generally exhibit these properties in greater or less degree. The severe pain which frequently attends diseases of parts supplied exclusively by the sympa thetic nerve, also affords still better evidence than can be derived from experifnents of the existence of sensory nerve fibres in the sym pathetic.