Morbid changes in the lungs after dividing the vagi.—The injury or division of the vagi is almost always fatal after a few days, even when precautions are taken to secure the free ingress of air into the lungs. The period of death in such experiments varies in different animals. Rabbits generally die earlier than dogs. The greater number of dogs die before the third day, and comparatively few live beyond the fifth day. In seventeen experiments upon dogs we found that eleven died before the completion of the third day, and seven of these eleven before the completion of the second day. Longet says that he performed this experiment on thirty dogs, and they all died on or before the fifth day, and none of the rabbits operated on, lived beyond thirty-six hours." Dupuy in his experiments found that horses lived to the fifth, sixth, and seventh day, when care %vas taken to admit a sufficient quantity of air into the lungs.tt De Blainville informs us that the pigeons on which he operated died on the sixth or seventh day ;II and in the experiments of Arnold§§ upon hens and pigeons, these animals died between the second and fifth day. In general the lungs are the only organs found in an abnormal state after death from injury or division of the vagi. We found the lungs unfit for the healthy performance of their func tions in fifteen out of seventeen dogs experi mented upon. These organs are almost always more or less congested with blood, especially at the depending parts, and the bronchial tubes and air cells frequently contain much frothy serum. In some portions of the lungs the congestion of blood is occasionally so great as to render them dense and devoid of air. This condensation is not unfrequently greater in some parts than what can be accounted for by the mere congestion of blood in the vessels, and probably depends in a great measure upon the escape of the solid parts of the blood into the tissue of the lung. The frothy serum has fre quently a greater or less deep tinge of red. Portions of the lung are likewise occasionally found condensed from pneumonic effusion. In seventeen experiments on dogs distinct evi dences of pneumonia were observed in five, and in two of these it had run on to gang-rene. These morbid changes upon the lungs are suffi cient to explain the imperfect arterialization of the blood, and the diminished evolution of internal caloric which precedes death. We have endeavoured to prove that these morbid changes in the lungs are the result of the dimi nished frequency of the respiratory movements which immediately follows the division of the vagi. The vagi are the chief excitors of the respiratory muscular movements, and when they are tied or divided the respirations are instantly diminished to less than half their former number. The flow of blood through the lungs is dependent upon the continuance of the respiratory process, and the great dimi nution in the activity of the respiratory muscular movements must be followed by a retardationi and congestion of the blood in the lungs. Such, a congestion of blood, as is well known, isl generally followed by an effusion of serum, and also predisposes the organsso circumstanced to various morbid changes, chiefly of an inflam matory nature. In the lungs this congestion is not only followed by the escape of the serum, but also of the more solid material from the vessels, rendering the tissue dense. The ef fused serum is mixed up with air moving along the bronchial tubes during inspiration and ex piration, and it thus becomes frothy. A little blood may also exude from the congested mu cous membrane of the bronchial tubes, giving the serum there effused a reddish tinge. As these changes proceed, the respiratory process becomes more and more imperfect, the blood flowing along the arteries approaches more and more to the venous hue, all the vital properties of the tissue are enfeebled, the internal tempe rature sinks, and the animal dies of protracted asphyxia. The division and other injuries of the pneumo-gastrics have no direct effect upon the production of the animal heat ; they only occasion this indirectly by enfeebling the func tion of respiration. We have elsewhere' ad.
duced evidence to sbew that these morbid changes do not necessarily follow the division of both vagi in all animals, and that the dog in a few rare cases may either die of inanition from the arrested secretion of the gastric juice and without any morbid alterations in the lungs, or may even survive the operation and recover from its effect.
Magendie, Wilson Philip," Mr. Swanit and
Longet,t. found that section of one vagus in duced diseased action in the lung of the same side. The lesions observed by these experi menters differed very considerably in their character. Dupuytren,§ on the other hand, could discover no alteration in the lung of the side on which the vagus had been divided in two dogs and a horse, though these animals were allowed to live more than a month. In an experiment made by Magendie before his pupils, the results were completely at variance with his former expressed opinions. The right lung of a dog was found perfectly healthy, though a portion of the vagus of that side was removed six months beforell We have re moved a portion of one vagus in seventeen animals, and allowed them to live a longer or shorter period,—from twenty-four hours to six months,--and in none of these could we detect any morbid changes in the lungs which we could attribute to the injury of the nerve. This immunity of the lung from the usual morbid changes, when one nerve only was divided, we attribute to the smaller diminution of the respiratory muscular movements, than when both nerves are divided.
Functions of the gastric branches. Do the gastric branches of the vagus contain wine. motiferous flarnents?—Mr. Mayo and Muller" failed in exciting muscular contrac tions in the stomach by irritating the trunks of the vagi, while this experiment succeeded in the hands of Bichat,ff Tiedemann and Gmelin,II and Longet.§§ Breschet and Milne Edwards inferred that muscular movements can be excited in the stomach of a living animal by galvanizing the lower end of the divided vagi in the neck from its effects upon the digestive process. NVe have carefully arid repeatedly performed the ex periment of irritating the vagi, and are confident that though it occasionally fails, yet it often suc ceedsllif These muscular movements in the sto mach differ considerably from those in the ceso phagus. They are more slow and are vermicular.
They generally commence at the cardiac orifice and proceed to a greater or less extent towards the pyloric orifice. Longet thinks that he can explain this discrepancy in the results of this experiment, as he found that it succeeded when the stomach was engaged in the process of chymification, and failed when it was empty. Though we are satisfied that the gastric branches of the vagus contain some motor filaments, yet we do not believe with Breschet and Milne Edwards, Brachet, Longet, and others, that the muscular rnovments of the stomach depend entirely upon the integrity of the vagi. Ma gendie observed these muscular movements continue after section of the vagi; and we ascer tained from experiment that if a dog recovers from the first effects of the operation of cutting the vagi, tbe stomach can still propel the chyme onwards into the duodenum. Arnold,-l- from his experiments upon hens and pigeons, con cludes that the contractions of the stomach are less influenced than those of the cesophagus and crop by division of the vagi. The grains taken into the stomach after this operation were found, however, to be considerably less bruised than in sound animals.
Effects of lesion of the vagi upon the sensa tions of hunger and sat iety.—Though the sensa tion of hunger is referred to the stomach, yet it is evident from well established facts that this sensation is actually situated in the encephalic portion of the nervous system. This sensation is not dependent, as far as .we know, upon any physical condition of the stomach itself, and in all probability arises from certain organic changes in the body, connected with the want of additional supplies of nutritious matters from without. Brachet relates two experiments to show that the sensations of hunger and satiety are arrested by section of the vagi,t but these are liable to certain sources of fallacy against which proper precautions were not taken. Four of seventeen dogs we experimented on, lived beyond the fifth day after the division of the vagi, and exhibited no sips of having lost the sensation of hunger ; on the other hand their actions indicated that they still retained this sensation. Longet has from his experi ments arrived at conclusions on this point similar to ours.§ There can be no doubt that the sensation of hunger is almost always sus pended for a longer or shorter time after the division of the vagi, probably occasioned in some measure by the pain and terror attending the operation, but if the animal live for a few days the sensation of hunger may return.