or less similar may often be traceable, as, for instance, in aneurisms.

We must conclude, then, that the rough grating quality of a murmur and the accompanying thrill are not due to any special state of the orifice at which the murmur is produced, but rather to the intensity of the murmur itself, and to the particular direction taken by the stream of blood which causes it.

Another modification of the bruit de souffle is that which is commonly spoken of in England as the "musical" murmur. It is a high-pitched sound, varying greatly in different cases, and resembling sometimes a whistle, sometimes the mewing of a cat, or the cooing of a dove, or, again, the note of some musical instrument. Savart studied this subject, but came to the conclusion that it is difficult to determine the conditions under which the sound produced by a vibrating liquid assumes a musical character.

According to Bergeon, there are at least two kinds of these murmurs-(1) Musical bruits produced by the vibrations of the fluid alone. (2) Musical murmurs produced in part by the vibrations of the fluid, in part by those of some solid body placed in the course of the sonorous veine fluide which it generates.

(1) Savart found that when a veine fluide is made to impinge upon a resisting surface with but little capacity for generating sound, a cube of wood, for instance, it spreads out, and radiating in all directions produces a musical sound. Now, Bergeon suggests that an arrangement is not unfrequently met with in the circulatory system which offers an approach to these conditions. It is that in which a vessel immediately beyond a narrowed point is bent in the form of an S. The veine fluide then impinges on one side of the vessel, and may fairly be supposed to radiate as in Savart's experiments. The spot to which Bergeon specially refers, as presenting the required curve, is the jugular fossa at the base of the skull. In anæmic subjects, he says, a veine fluide is often generated at this point, as had been shown by M. Bondet, and, reinforced by the S-shaped curve of the vessel, it gives rise to an intolerable singing in the ears.

(2) A more frequent cause of the musical bruit is probably the vibration of a membranous substance suspended in the blood stream. This kind of bruit appears to be very easily imitated. Bergeon found in his experiments that by introducing a small tense membrane into a tube just beyond a narrowed point, so that the veine fluide might impinge upon it, he could throw this membrane into vibration, and make it produce a sound which was sometimes louder than that of the veine itself. By Chauveau musical bruits have even been produced experimentally within the jugular veins of the horse. He first nar

rowed a vein at one spot, so as to generate a vibrating veine fluide, and afterwards seized the free edges of the valves with small bent pins, and according as he allowed the valves to float in the blood stream, or kept them applied to the wall of the vessel, he found that a musical bruit was present or disappeared again.

The theory of the veine fluide, which we have been tracing in its applications to cardiac and vascular murmurs, is by no means confined to them. It has an equally important bearing upon the sounds that are heard with the respiration under healthy and morbid conditions. The French writers, whose works we are reviewing, have not failed to study this branch of the subject as well as the former. And we may now pass on to consider the conclusions to which their experiments and observations have led them.

But first it may be asked, whether Savart's laws are applicable to gases as well as to liquids. To this question a sufficient answer might, perhaps, be found in the fact that the sound made by an ordinary bellows is so exactly like the cardiac and vascular murmurs that we have been considering that it has given a name to them, in both the French and the English languages-bellows murmur-bruit de soufflet. The point has, however, been specially investigated by Sondhauss.1 He experimented with a jet of common air, mixed with tobacco smoke, to make it visible. This was forced by means of a bellows into a glass vessel through a narrow orifice. For a distance of three centimètres from the orifice the jet retained as nearly as possible its size, being, in fact, somewhat smaller. Beyond this it became wider than the orifice, and appeared to be the seat of a continual agitation. When made to impinge upon a spherical or plane surface the jet spread out and formed a sheet. In other words, Sondhauss's experiments with gases afforded results identical, so far as they went, with those of Savart on liquids.

It may, therefore, be assumed that whenever a stream of air passes from a narrow into a wider space a sonorous veine fluide may be generated.

Now, during the act of inspiration, the air drawn into the mouth and nose enters successively passages that are smaller and smaller until it reaches the space between the true vocal cords. Through this comparatively narrow space it passes into a much wider one, the trachea. The conditions for the production of a sonorous jet are thus fulfilled. And on listening over the larynx and trachea of a healthy person one hears, each time he

1 Poggendorff's Annalen,' 1852, p. 58.

inspires, a loud blowing sound, which evidently is due to this cause. It is carried for some distance downwards along the respiratory passages, and thus follows the law of transmission of reine fluide.

a

In the act of expiration, again, the air traversing the upper opening of the larynx escapes from a narrow into a wider space, so that a sound is in all probability produced at this spot. And if the lips be partly closed, while the expiration is at all forcible, another sonorous jet is generated as the air passes out of the mouth. Now, it has been shown that the sound produced by the vibrations of a veine fluide is heard chiefly in the direction taken by the jet itself, and is but slightly, or not at all, audible behind the narrowed point at which the veine fluide is produced. Bnt on listening with the stethoscope over the upper part of the trachea of a healthy person, one finds that an expiratory sound is plainly audible, and is, in fact, louder than the inspiratory sound heard at the same spot. The explanation of this appears first to have been given by Bergeon. He shows that the expired air, in passing through the larynx, meets with the edges of the superior or false vocal cords, which, with the base of the epiglottis, form projections directed against its stream. The result is the same as in those experiments of his, in which a current of water flowing through a tube was made to pass into a narrowed part that projected backwards, forming a lip or rim, and giving rise to a circular cul de sac, facing the current. Under these conditions, as we have seen, a sound is produced, which (unlike that of a simple veine fluide) is heard behind the seat of obstruction. It has already been shown that the results obtained by Bergeon in these physical experiments are paralleled by the murmurs that are audible over the aorta in aortic regurgitation, and over the left ventricle in mitral regurgitation, respectively. The expiratory sound heard over the trachea appears to be another striking instance of the same kind. Indeed, as Bergeon remarks, there is no other way of accounting for the fact that the tracheal expiratory sound should be louder than the inspiratory. For, since the stream of air in expiration moves more slowly than in inspiration, the former ought to produce a more feeble murmur than the latter, did the two murmurs arise in the same way. But it is an ascertained fact that the sound produced by a current impinging on a solid edge turned against it is proportionately louder than that due simply to a veine fluide.

Now, if the stethoscope be placed over the surface of a healthy

1 All authors appear to admit this, so far as the human subject is concerned. M. Bondet however, speaking of the horse, says that the expiratory murmur over the trachea is often less accentuated though longer than the inspiratory.

person's chest, a soft rustling sound is heard during inspiration, but during expiration either no sound is heard at all, or one which is comparatively much less loud. By Laennec this and the other respiratory sounds that have been already mentioned were attributed to the friction of the inhaled air against the walls of the trachea, bronchial tubes, and pulmonary vesicles, respectively. Most subsequent writers have expressed similar views.

But, as some of our readers may be aware, a very different theory was promulgated by the late M. Beau. As far back as the year 1834 that ingenious but eccentric physician maintained that the chief cause of the various respiratory sounds heard by auscultation is the transmission downwards of a sound which he termed the "bruit guttural," and which he believed to be due to the friction of the in- and out-breathed air against the parts at the back of the throat, and especially the velum palati. Subsequently, in a second paper on the same subject,2 M. Beau attributed the formation of the sound in question mainly to the orifice of the glottis, and accordingly named it the "souffle glottique."

Soon after the promulgation of M. Beau's theory, it was critically examined by Dr. Stokes and Dr. C. J. B. Williams. The former rejected it, mainly on the ground that a natural respiratory murmur can be heard in patients who do not breathe through the mouth or nostrils, but through a tracheal fistula. The latter also refused to accept it, using the following arguments:-(1.) That the sound of the voice, which is much stronger than the inspiratory murmur, does not reach many parts of the surface of the lungs. (2) That vesicular respiration may be so exaggerated in parts as to become as loud as the tracheal, without (this having sustained any proportionate increase. (3) That when laryngeal rhonchus supplants the ordinary laryngeal blowing we still have the vesicular murmur, with the addition of the distant laryngeal rhonchus.

Raciborski, also, appears to have combated M. Beau's theory, showing that in the rabbit after tracheotomy the respiratory sounds are heard as before. But, as was said by Dr. Spittal5 (in

"Recherches sur la Cause des Bruits Respiratoires perçus au moyen de l'Auscultation," Archives Générales de Méd.,' 1834, p. 557.

2 Archives Générales de Méd.,' 1840.

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3 Treatise on the Diagnosis and Treatment of Diseases of the Lungs,' 1837, p. 252.

'Pathology and Diagnosis of Diseases of the Chest,' fourth edition, 1840, p. 22 (note).

5 Edin. Med. and Surg. Journ.,' 1839, li, p. 99. The statement in the text with regard to Raciborski is taken from this paper, as we have had no opportunity of consulting Raciborski's work.

a paper defending M. Beau's views), this experiment can hardly be regarded as conclusive, for the open extremity of the tube may have been itself sufficient for the production of a murmur, which would be transmissible downwards exactly like the bruit guttural. The same remark evidently applies to Dr. Stokes's observation. Indeed, with the views that we now hold as to the causes of the development of the veine fluide, it is evident that a tracheal fistula presents all the conditions requisite for it.

The modern French writers, however, whose works we have under review, appear to have demonstrated conclusively the truth of the opinion generally held, that the respiratory sound heard on auscultation over the surface of the lungs is developed within the organs themselves, and not merely transmitted downwards from the larynx; and this by two distinct lines of argument. In the first place, they have repeated Raciborski's experiment under such conditions as to exclude the possibility that a veine fluide could be generated in the tracheal wound. The trachea was completely divided between two of its rings, and its open end was drawn outwards either by a hook or by a metallic suture. The result was that the "bruits glottiques disappeared entirely. On the other hand, the inspiratory murmur still remained audible over the surface of the chest, and its intensity was but little, if at all, diminished. The laryngeal sounds may therefore be abolished, while the pulmonary inspiratory murmur persists.

In another series of experiments, made by M. Bondet, exactly converse results were obtained. The pulmonary murmur was extinguished, the laryngeal sounds remaining unimpaired. This result was effected, in the horse, by the division of the pneumogastric nerves. After the performance of this operation, the acts of respiration were generally found to be less frequent, but the respiratory movements, nevertheless, more ample. The amount of air drawn in was increased, as was shown by the spirometer; being in fact, double the normal quantity, or even more than this. Now, on listening over the trachea the respiratory sounds were found to be very loud and prolonged, especially the inspiratory. But the pulmonary murmur was completely abolished. M. Bondet states that he repeated this experiment several times, and always with the same result. On listening to the chest of animals after section of the pneumogastric nerves, there was absolute silence.

Of the fact just stated M. Bondet gives the following very ingenious explanation. It is well known that an immediate effect of section of the pneumogastric nerves is paralysis of the muscles of the bronchial tubes. One of the first consequences