and are distributed over certain viscera in the thorax and abdomen. This singular destination indicated something peculiar in the functions of the parts to which they are appropriated, while, at the same time, the form and situation of the nerves rendered them particularly favourable for investigating the uses which they serve, as it was easy to deprive the organs of the nervous influence, without the risk of injuring the parts, or affecting them in any other manner. We accordingly find that the division of the par vagum is among the oldest of the physiological experiments that are upon record.

In consequence of the connexion which these nerves have with the recurrents, the effects of their division have been often confounded together, and it was not until comparatively of late years, that we were aware of the difference between their functions, or attempted to separate them from each other. We now know, that by dividing the recurrent nerves, the action of the glottis is deranged, and the voice destroyed or materially impaired, and this was supposed by the ancients to be the chief effect of dividing the par vagum. It was found, however, that other functions were injured, particularly the circulation, the respiration, and the digestion, and that death was, sooner or later, the consequence of the operation.'

1 We shall find a very considerable degree of irregularity in the results of the experiments that have been performed on the division of the par vagum. In most cases the death of the animal, or the destruction of some important function, being the evident and direct consequence of the operation, while, in some instances, little more appears to have ensued from it, than

The earlier among the modern physiologists appear, for the most part, to have directed their attention to the effects that were produced upon the heart, and, for a long time, the principal subject of discussion was how far the division of the nerves suspended or destroyed the action of this organ. But although many experiments were performed, and their effects described, the observations were not made with that degree of accuracy, which can enable us to draw any correct deductions from them, nor indeed were the observers themselves aware of the circumstances which it was necessary to attend to, in order to attain a full insight into the subject.2

what might be referred to the pain and irritation produced by the operation. These anomalies are probably, in a great measure, to be referred to the very curious discovery of Dr. Philip, to which I have already alluded, v. i. p. 253, that when a nerve is divided, and the ends remain in opposition, or even when they are separated from each other by a small interval only, the nervous influence continues to be transmitted along it with little or no interruption.

2 We have a very interesting historical detail given us by Legallois of all the experiments which have been performed on the par vagum, from the time of Rufus (who appears to have been the first anatomist, who tried the effect of dividing or compressing these nerves) to the date of his own publication in 1812. I have thought it sufficient to notice those only which were made for the purpose of establishing some new principle, or which lead to some important conclusion. See his work "Sur le Principe de la Vie," p. 164 et seq. See also Mr. Broughton's sketch of these experiments, prefixed to his paper in the Quart. Journ. v. x. p. 292. We have also a list of the authors, with references, in M. Breschet's paper in "Archives de Medecine," Aug. 1823.

One of the earliest among the moderns, whose ideas respecting the nervous system assumed a more matured form, was Willis. He divided the par vagum, in order to obtain a test of the truth of his doctrine, that the involuntary motions of the body proceed more immediately from the cerebellum, and having found, in conformity with his preconceived opinion, that the circulation was considerably affected, he did not particularly attend to the effects of the operation upon the other organs.3

Haller's experiments led him to suppose, that the stomach and the lungs were the organs that were more immediately affected by the division of the par vagum, but he has not explained how the effect is produced, what relation the parts bear to each other, or how they act in causing the death of the

3 Cerebri Anat. cap. 24. p. 127. It may be interesting to recite the names of the physiologists who successively occupied themselves with this inquiry, for the purpose of showing the great interest which was attached to it. The following list is taken from Legallois, p. 170; Chirac, Bohn, Duverney, Vieussens, Schrader, Valsalva, Morgagni, Baglivi, Courten, Berger, Ens, Senac, Heuermann, Haller, Brunn, and Molinelli; it appears that, in these cases, the circulation was the function that was more particularly attended to, and that, in a great measure, with reference to Willis's hypothesis. To these may be added Riolanus, Plempius, Lower, and Boyle, who preceded, or were contemporary with, Willis; Haller refers to his relative Brunn, as having performed many experiments on the par vagum. Haighton's experiments on these nerves will be noticed in a subsequent section.

4

animal. With respect to the circulation, it seemed to be the general opinion, that the derangement produced in this function was neither so considerable nor so uniform as it should have been, had the heart been the part primarily affected. And with respect to the stomach, although perhaps no organ seemed to sustain more injury, yet life was destroyed more rapidly than it would have been, had the digestion alone been the function that was suspended.

The lungs were therefore concluded to be the organ, the derangement of which was the immediate cause of death, an opinion that seemed to be confirmed by some experiments of Bichat's, and now the discussion took place respecting the mode in which the division of the par vagum could act upon the lungs, so as to prevent them from performing their functions. A number of experiments were accordingly made to elucidate this point, which, in consequence of the improved state of physiological science, and of the greater dexterity and precision of the operators, were attended with results, that are much more interesting and satisfactory than those of the older anatomists. We are chiefly indebted to the ingenuity and diligence of the French physiologists for the information which we possess upon this topic,

4 Haller's experiments are contained in his work "Sur la Nature sensible et irritable des parties du Corps animal;" No. 181, 182, 185, 186, 188. His opinion respecting the effect of the operation is stated in El. Phys. iv. 5. 2.

5 Sur la Vie &c. p. 2. Art. 10. § 1. p. 221..224.

and more particularly to the investigations of Dupuytren, Dumas, Blainville, Provençal, and Legallois."

The points that were more particularly attended to were to ascertain what is the exact state of the lungs, whether they receive the air as usual into their cavities, and whether the same chemical change was induced upon the air as in ordinary respiration. A preliminary step of the investigation, the importance of which seems to have been first duly appreciated by Legallois, was to distinguish accurately between the effects which ensued from dividing the par vagum and the recurrent nerves; this he accomplished by opening the trachea below the glottis, só as to ensuré a free passage for the air into the bronchia. The result of the investigation appears to be, that the vessels of the lungs are loaded with blood, and the bronchial cells clogged up with a serous or mucous effusion; that the air is of course only partially

See Legallois' work, p. 177. et seq. Blainville, although he observed that a certain degree of derangement took place in the lungs, appears to have considered it as not an essential effect of the operation, and ascribed the death of the animal to injury sustained by the functions of the stomach. Ubi supra, p. 181. Sæmmering, Corp. Hum. fab. t. iv. p. 237. remarks that the compression of these nerves by a ligature produces difficulty of breathing, deafness, vomiting, and that it prevents the food from being digested.

7 Or perhaps rather the laryngeal nerves, as we are informed by Dr. Hastings, that, in his experiments, he found little or no dyspnea by dividing the recurrent nerves, but that it took place immediately upon dividing the laryngeal nerves; Philip's Inq. p. 121, note.

Sur le Principe de la Vie, p. 188. et seq.; p. 205. et seq.