Experiments on the section of the glossopharyngeal and hypoglossal nerves of the frog, and observations of the alterations produced thereby in the structure of their primitive fibres

Abstract

After describing the natural structure of the tubular fibres of the nerves, the author states the results which he observed to follow the section of the nerves of the frog’s tongue. To this organ two principal pairs of nerves are distributed; one of these, issuing from the cranium along with the pneumogastric and distributed to the fungiform papillæ, is regarded as the glossopharyngeal; the other, arising from the anterior part of the spinal cord, and passing through the first intervertebral foramen, the author (following Burdach) names the hypoglossal. Section of the glossopharyngeal nerves does not cause any perceptible loss of motion or of common sensa­tion, and this fact, together with its distribution to the fungiform papillæ, leads the author to consider this nerve as the nerve of tasting. On the other hand, when the hypoglossal nerves are divided, the tongue is no longer sensible to mechanical irritation, and its motions are entirely abolished. Simultaneous division of the right and left glossopharyngeal nerves is followed by the death of the animal in a few days, and the same effect ensues after division of both hypoglossals. This result, which takes place more speedily in summer than in winter, the author is disposed to ascribe to a disturbance of the mechanical process of respiration, in which, as is well known, the muscles of the frog’s mouth and tongue take a large share. To ascertain the changes which take place in the nerve-fibres after division of the trunks to which they belong, the operation was confined to the nerve of one side only, and the fibres of the unin­jured nerve of the other side served for comparison. These changes ensue more speedily, and go on more rapidly in summer than in winter, commencing usually in about five days. The pulp contained in the tubular nerve-fibres, originally transparent, becomes turbid, as if it underwent a sort of coagulation, and is soon converted into very fine granules, partly aggregated into small clumps, and partly scattered within the tubular membrane. These granules are at first abundant, and render the nerve-fibre remarkably opaque; but in pro­cess of time they diminish in number, and, together with the inclosing membrane, at length disappear, so that at last the finest ramifications of the nerves which go to the papillæ, or those going to the muscular fibres of the tongue (according to the nerve operated on), are altogether lost to view, in consequence of the destruction and eva­nescence of their elementary fibres. The disorganization begins at the extremities of the fibres, and gradually extends upwards in the branches and trunk of the nerve. The other tissues of the tongue remain unaltered. When the cut ends of the nerve are allowed to reunite, the process of disorganization is arrested, and the nervous fibres are restored to their natural condition. The author ascribes the disorganization and final absorption of the nerve-fibres to an arrestment of their nutrition caused by interruption of the nervous current, and considers his experiments as affording most unequivocal evidence of the dependence of the nutrition on the nervous power.