Notes and observaation on diseases of the heart and of the lungs in connexion therewith

Front matter

NOTES AND OBSERA^ATIONS

ON

DISEASES OE THE HEART

Preface

The following pages, having reference to tlie more ordinarilyoccurring diseases of the heart, represent the mode, used in their investigation, which an extended experience has shown to be useful for practical guidance.

Dming the last forty-seven years my opportunities for observation have been extensive. In 1827, in conjimction with the late Mr. Eobert Spittal, author of "A Treatise on Auscultation, 1830," my attention was specially directed to the study of pectoral diseases. We were then feUowstudents and clinical clerks in the wards of the Koyal Infirmary of Edinburgh, under the late Doctors Home, Graham, and Alison, the then very eminent Professors of Clinical Medicine to the University. In 1830 I enjoyed the advantage of further prosecuting this study in the wards of the Hopital de la Pitie, in Paris, under the immediate guidance of the late Baron Louis, one amongst the many very illustrious physicians that France has produced. Since then, besides an extensive acquaintance with the occurrence of disease in private lil'e, I have occupied the position of viii

PREFACE.

Pliysician to the Exeter Dispensary, and to the Devon and Exeter Hospital. This latter position I still retain.

These several spheres of observation have ' afforded me opportunity of accumulating the records of a large number of cases.

In the course of the foUowing pages reference to some few of these cases has been speciaUy, but briefly, made. As a general rule, it has appeared to me to be more useful not to enter into any minute detail and transcript of cases, but to state solely the conclusions to be drawn from them.

It had been my wish, and my intention, to have endeavoured to determine with precision some of tliese conclusions, l:)y referring the cases, with post-mortem examinations, to the test of the numerical method. But this mode of investigation I was obliged to abandon, for I soon found there was an absence of so many elements, necessary for the attainment of accurate and reliable results, as to render deductions thus made, unsatisfactory, and perhaps misleading.

The details of post-mortem examinations may be, in themselves, sufficiently trustworthy, but before the physician can venture to deduce from them any positive or scientific conclusions, it is especially necessary for him to know the relative amount which the cases thus examined bear to those not examined under similar, as well as different, circumstances of antecedent disease; and also to those in which the presence of these diseases, though existing, may not have been ascertained ; then — many diseases, that have been latent for years, suddenly burst into activity, and it is difficult, after death, to

TKEFAUE. , iX

decide to wliat period of the disease the origin of the morbid couditious belongs ; so also, during life, the physician often fails in ascertaining the origin of disease both as regards time and cause, in fixing and appreciating the true sequence of events, and in separating the complications of one lesion from another. All these difdculties serve to make deductions from a limited amount of observations, by the numerical method, deficient in necessary precision; and imperfect and unreliable statistics offer but unsatisfactory and dreary reading.

Many examples of rare and curious heart disease have passed beneath my observation. The consideration of these I have not ventured upon:— seeing that they yielded no certain nor reliable signs of their existence, the enumeration of their details would have failed in practical results.

Some apology is due for the order and mode in which the matters of the following pages have been treated. I am aware they have the aspect of being somewhat fragmentary, and deficient in scientific completeness. Still I hope they may prove of some small service, by way of suggestion, to my younger professional brethren, in which case I shall consider myself amply repaid for the trouble, and the expense of time, the preparing them for the press may have cost me.

The BAENlflELD, EXETEE,

Contents

I-AOE

Peefacb , , , . yii — ix"

CHAPTEE I.

CHAPTER II. SOUITDS OF THE HeAET 8 — 27

Described, 8 ; synchronous with closure of valves, 9 ; theories of, 9 ; hydi-aulic origin of, 12 ; illustration from Ai-nott, 12 ; Dr, Leared's theory {note), 12 ; law of murmurs, 18 ; rhythmical action of heart, 20; its influence in causing tho sounds, 20.; in causing murmurs, 24 ; mitral and tricuspid murmurs, 24 ; force requisite for sounds and murmurs, 25 ; semilunar murmur, 25 ; seat of murmur determined, 26.

XII

CONTENTS.

UHAPTEU Hi.

NoMUcil souuda absent, others present, 28 ; quality of sounds, 29 ; how moJmoJ, 30; iu fevir, 30; confu.sod by excitement, 31 ; by respiratory sounds, 32 ; by friction sounds, 33 ; by extrinsic pressure, 34 ; by pericardial effusions, 35; by malformation, 36; sounds reduplicated, 37 ; reduplication explained, 38 ; how produced, 39.

CHAPTEE IV.

Endocaediai MuEMims ; theie Diagnosis and its Difficulties . 41 — 61

Murmurs confused by weakness, 41 ; by pulmonary rales, 41 ; by friction sounds, 42 ; by murmur in arteries, 43 ; occasionally cease, 43; cause of, 44 ; chieiiy in left heart, 44 ; presystolic, 4o ; orig^in of, 46 ; systolic mitral, 47 ; confused by aortic murmur, 48 ; aortic systolic and regurgitant murmurs, 48 ; pulmonafy semilunar valve murmur, 49; tricuspid regurgitant, 49; diagnosis difficult, 49; hsemic or blood murmurs, 50 ; systolic basic murmur of fever, 61 ; valvular disease without murmur, 51.

CHAPTER V.

The Pulse : its Physical Oeigin ,52 — 68

Described, 62 ; theories of, 54 ; definition of, 66 ; phenomena and their cause, 56 ; sphygmograph, 58 ; qualities of arteries, 58 ; wave of blood, 59 ; action of heart on, 61; velocity of blood wave, 63; vibrations of pulse independent of forward wave, 64 ; circulating wave and p\ilse separate, 65 ; arrest of flow wave cause of pulse, 66; indications of s^jhygmograph, 67.

CONTENTS.

xni

CHAPTER VI.

Ctenerai, Prognosis from Sounds, MuEMtiES, and PrasE . . C9-

VahiUar sounds, 69 ; when hpalthy, 69 ; when diseaned, 70 ; valvuhvr murmurs, 71 ; indications of pulse, 72 ; varieties of described, 74 ; diagnosis from, 76.

CHAPTER VIT.

Eeroes in the Impulse of the Heart 78 143

Fimctional and organic diseases, 78 ; diminished impulse, 79 ; indications of, 80 ; conditions of heart, 80 ; dilatation, 81 ; and thinning, 82 ; dilatation of right ventricle, 83 ; adherent to pericardium, 84; fatty infiltration, 85; symptoms of, 86; haemorrhages, 87; hypochondriasis, 88; prognosis in, 90; sudden death in, 90 ; treatment of, 90 ; pericardial effusions, 91; diminished impulse from small heart, 92; symptoms of, 92; fatty metamorphosis, 93; atrophy, 93 ; muscular weakness, 94; descending and ascending respiration, 96 ; arcus senilis, 98 ; difference in anaemic and dilatation weakness, 98; prophylaxis, 99 ; treatment, 99 ; asthenic diminished weak impulse, 101 ; functional weak impulse, 103 ; treatment, 104; impulse increased, 105 ; position of ictus ventriculi, 107; area of impulse, 109; hypertrophy. 111; hypertrophy with dHatation, 111 ; dilatation, 112 ; adherent to pericardium, 112; differences between hypertrophy and dilatation, 112; with valvular disease, 113; symptoms of hypertr^hy, 114; compHcations, 116; symptoms of dilatation, 118; anatomical condition of hypertrophy, 120; of dilatation, 120; connective tissue hypertrophy, 121; prevalence of hypertrophy, 122: influence of age, 122; sex, 122; relations of dilatation to hypertrophy, 123; relative liabiHty of different parts of heart, 123 ; causes of increased impulse, 124; of hypertrophy, 124; shortness of breathing, 126; effects of, 126; prognosi.s, 127; prophylaxis, 1 28 ; treatment, I29' functional increase of impulse, 130; symptoms of, 131; compKcations, 135; cause of , 137: prophylaxis, 142; treatment, 142.

xiv

CONTENTS.

CHAPTER VIII.

PAOK

Eeeoes in the Rhythmical Action of the Heart . . . 141—168

Theories of rhythmical action, 144 ; errors of, 147; origin of, 149; nervous, 149 ; muscular weakness, 149 ; in hypertrophy, 151 ; hypertrophy with dilatation, 151 ; walls weak, 152 ; valvular deposits, 152 ; in fever, 152 ; in inflammatory diseases, 153 ; in rheumatism, 155 ; rupture of valves, 157; diseased valves, 157; in functional diseases, 158 ; normal irregularity, 159 ; prognosis in, 160; causes of, 161; effect of tea, 162; predisposing causes, 162; syncope, 163; symptoms of, 164; exciting causes of, 165; nervous origin of, 168.

CHAPTER IX.

The Pathological Indications of Endocardial Mttemttes . . 169—198

Organic murmurs, 169; alteration of murmurs, 170; suppression of, 171; indications of, l7l ; induced by endocarditis, 172; chronic forms of, 173; rheumatic influence, 173; gouty, 173; congestive diseases, 174 ; not the cause of hypertrophy, 174 ; hypertrophy and valve disease, same origin, 176; valvular disease compensation, 177 ; effects o^dilatation on valves, 177 ; effects of force on valves, 178; anasmic murmur, 179; symptoms, 180; in chlorosis and spansemia, 180 ; symptoms of, 181 ; exophthalmos, 181 ; causes of chlorosis and spansemia, 182 ; origin of, 183 ; flow mitral mm-mur, 184; regurgitant mitral miirmui-, 185; symptoms of, 186; consequences of, 187 ; presystolic mm-mur, 189 ; causes of mitral valve disease, 190 ; treatment of, 190 ; aoi-tic valve disease, 191 ; causes of, 191 ; symptoms of, 192 ; effects of, 193 ; prognosis, 194 ; prophylaxis and treatment, 195 ; triscupid valve disease, 195 ; systolic murmur, 196; symptoms of, 196; cause of, 197: prognosis and treatment, 198.

CONTENTS.

XV

CHAPTER X.

PAGE

Pain of the Hilvet 190 — 212

Pain defined, 199 ; pain with inflammation, 200 ; nervous, 200 ; forms and seat of, 201 ; symptoms of, 202 ; cause of, 202 ; prognosis and treatment, 203 ; angina pectoris, 204 ; symptoms of, 204 ; causes of, 204 ; cases ef, 206 ; theory of, 207 ; immediate cause of, 208 ; dumb angina, 209; in drowning, 210; treatment, 210 ; nitrite of amyl, 210.

CHAPTER XI.

Diseases of the Ltjnqs in Connexion with Diseases op the

General statement, 213 ; pneumonia, 214 ; emphysema, 215 ; anatomical characters of, 216; symptoms, 216; consequences of, 217; oedema, 218; hronchitis, 219 ; caused by valvular disease, 220; phthisis, 222 ; anatomical changes in, 222 ; cyanosis, 223 ; bronchial artery murmur, 223 ; cause of, 224 ; seat of, 225 ; errors of respiration, 226.

CHAPTER XII.

Summabt and CoNCLirsiON 228 234

Relative fataUty, 228 ; disease though sHght may have serious consequences, 231 ; communications made to friends and patient, 232 ; life assurance in, 232.

i

NOTES AND OBSEEYATIONS

ON

DISEASES OF THE HEART.

CHAPTEE I.

CIRCULATION OF THE BLOOD.

An extended practical acquaintance with diseases of the heart cannot fail to have exhibited to the careful medical observer the very remarkable fact that analogous, if not absolutely similar, departures from the normal physical conditions of this organ may exhibit in different people very different results; in some cases they prove to be associated with fatal tendencies, in others to be consistent with a sfood average state of health and prolonged life; whilst in other cases a fatal termination may unexpectedly occur, though yielding but few, or even no indications of disease, to the most anxious physical investigation.

It may be assumed that those more obvious physical phenomena which the heart reveals, whether to touch, to careful percussion, or to the attentive ear, as differing from what is usual in health, are due to departures, perchance temporary only, from the normal condition of this organ; but it may also be concluded, where these phenomena are found to be persistent, that they are due to alterations, as the case may be, in its structure or bulk, or to disarrangements of its valvular completeness.

B

^ CIRCULATION OF THE BLOOD.

These structural alterations generally entail, sooner or later by themselves, or by their distui-bance of the animal economy, a fatal termination. Nevertheless, conspicuous and very remarkable exceptions occasionally jDresent themselves, and the issues of Ufe or death do not appear to be influenced by the inferred condition of the heart; wliile, on the other hand, accidental or temporary departures from the normal condition may present themselves as very dangerous, and perhaps immediately fatal, affections. Again, fatal cases are occasionaUy met with, and wliich appear to be due to structural alterations scarcely, if at aU, appreciable by carefid examination, or, at any rate, to such as neither alter the size of the heart nor impede its blood-flow.

It is proposed, by reference to the notes of a considerable number of cases, to review some of the affections belongmg to these several categories, and chiefly with the object of considering and determining their relative fatal tendencies. But, before doing this, it is proposed to say some few words respecting the action of the heart, in its relations to the circulation of the blood, and of the sources of the normal and abnormal sounds emitted thereby, as also respecting its influence on the pulse.

As regards the heart, it has appeared to me that the view of its action has been unnecessarily — I wovdd even say erroneously— complicated by the general statement that the function of the auricle is that of the "propeller" of the blood into the ventricle. The simpler view that I would hazard is, that the ventricle is essentially the organ that, on the one hand, by a gradual screw-lilce expansion sucks in the blood, and, on the other, by a gradual screw-like contraction expels it; that the j)roper function of the auricle is, on the one hand, to contain a ready supply of blood for the expanding ventricle, and, on the other, a safety-pouch to counteract or equalize the backward strain caused by the closure of the auriculo-ventricular valves.

I have elsewhere {Medical Gazette, Dec. 5th, 1857) ventured

ACTION OF THE HEART, to state that, as regards the heart, the circulation of the blood is more simply effected than is usually considered to be the case; that, in fact, the heart proper is ventricvdar and ventricular only; and that the circulation of the blood through the heart mainly depends upon, firstly, its ventricular exhaustion or suction power ; and then, secondly, on its ventricular contraction, whereby it is indued with the function of propulsion.

The auricle, on the other hand, is rather to be considered as an appendage proper to the venous system, and not as appertaining or necessary to the ventricular heart,* and that, therefore (without ignoring the influence, as propellers of the blood, of the capillaries and of the veins generally, feeble though this influence may be, as also of the auricle, as portion of the venous system), auricular contraction is not an active agent in the movement of the blood.

The above conclusions are grounded on the fact, that the distension, or greatest size, of the auricles is not induced by a sudden influx of blood from the cavte or pulmonary veins, but on, and by, the final act of contraction of the ventricles, when there arises a retrograde pressure against the ever onward flow of blood from the venous system. This retrograde pressm-e is caused primarily, on the closure of the auriculo-ventricular apertures, by the floating up _q£. the tricuspid and mitral valves, and subsequently by these being propelled be-- yond the auriculo-ventricular axes into the auricles; hence the blood then contained within the auricles is ponded back upon that flowing into them, and their greater distension efl-ected. The relaxing of the valves on the expansion or diastole of the ventricles, whereby the exhaustion or suction

, * borne out by the anatomical fact stated by Pettigrew {Edinhurah

Medial Journal Aprf 1873) : "The auxiculo-ventxiclr fibrous LJZl beeuyanously described, the majority of investig-ators regarding them as strongly pronounced structures, which afford attachment, not only to th" valves, but to aU the muscular fibres of the auricles and ventricles. A one ful exammation of these rings in boiled hearts has led me to a different" conclusion. They afford attachment to the muscular fibres of the af des and to the valves, h,a to almost none of the mn.cnlar fibres of the ve^trielesf'

R 2

CIRCULATION OF THE BLOOD.

power of the heart is exercised immediately, relieves the auricles of this amount of tension, and they partially collapse as the blood is first drawn from them into the ventricles, on the gradual uncoiling and screw-like expandings of these latter immediately after their final, sudden, and energetic act of contraction has been concluded. Their normal condition of filled but not distended vessels is then restored. In this state, by a kind of vermicular or peristaltic movement, they continue to receive blood and to deliver it into the rmcoiling ventricles, till these latter, being again filled, again contract upon their contents, and so again raise the opposing valves.

Probably, during these several processes, the fluid supplied to the auricles and ventricles is so evenly balanced that the pericardium contains, at no one time, a differing amount of contents.

Though not entirely ignoring some muscular consent in the auricles, their normal quality appears to be that of elastic tubes or vessels, capable, mthin certain limits, of exercising the functions of expansion and contraction. In accordance, therefore, with the varying amounts of fluid supplied to them, they exemplify the phenomena of dilatation and contraction by elasticity rather than by dynamic muscular contractility ; while the ventricles distinctly exemplify this latter. It should be here borne in mind that the auricles are furnished with a large relative amount of the elastic layers of the endocardium, and that the musculi-pectinati are fewer and weaker in the left than in the right auricle. Moreover, the thin and fragile structure of the semilunar, as compared with the tricuspid, and mitral, valves, strengthened as these latter are by the musculi-papiUares, columnaB earner, and chordse tendinese, and their sole function being that of preventing regurgitation from the aorta, show them to be fitted, neither by position nor in structure, to resist the strain of a violent propulsion of fluid from the auricles into the ventricles ; while the suction power of these latter, during their systole, is precisely such as calls the special function of these semilunar valves into active usefulness.

The very careful and valuable experiments of Dr. Halford,

FUNCTION OF THE AURICLES.

and, previously, of Peclilin and others, fully confirm the above conclusions ; for the ventricles were seen to expand as well as to contract, though no blood was furnished to them. Expansion, and hence a suction-power, being, therefore, a function as normal to them as the recognised one of contraction, and by the aid of which it is universally allowed they are endowed with the power of propulsion.

Supposing the above view of the function of the auricles to be correct, it is then probable that in addition to the support afforded by the strong and unyielding pericardium, the musculi-pectinati act firstly in preventing undue distension ; and secondly, after distension has been effected, in aiding towards restoring the auricles to their normal dimensions.

The above, doubtless, is not in accordance with the ordinary explanation of the function of the auricles, which is, that the auricles contract on the blood contained within them, and thus propel it into the ventricle. There are three cogent arguments against this conclusion. Firstly, it would assume that the auricles contained an amount of blood which should be more than equal to the capacity and requirements of the ventricles on their expansion, and this, seeing they are never entirely emptied, they cannot be said to do ; secondly, the absence of a normal and regularly recurring blood wave in the jugular and larger veins ; and, thirdly, the absence of any sufficient valvular apparatus at the venous extrances to the auricles, with the exception of the valve of Thebesius, which only prevents regurgitation into the coronary vein, and this is only effected, by the elongation of the membrane forming it, at the moment of the greatest distension of the auricle on the closure of the tricuspid valve. Doubtless in the right auricle there exists the Eustachian valve; and, in the left auricle, the pulmonary veins on their entrance are surrounded by muscular fibres. But these structures do not present the adequate perfection of valvular mechanism; moreover, as age advances, the Eustachian valve becomes conspicuously deficient for all closing purposes.

This valvular, deficiency would alone militate against thei

CIRCULATION OF THE BLOOD, assumption that the function of the auricles was essentially and XDrimarily that of djniamic propulsive power ; for not only is the absence of any such structural arrangement to such an end contrary to the whole principle of the circulation and the mechanism of its organs, but, in fact, the contraction of the auricles would as equally force the contained blood into the cavae and the pulmonary veins as into the ventricles.

That the suction power of the expanding ventricle is adequate to produce a current in the larger veins, may be assumed by the murmur produced by pressure on the jugulars ; wliile the phenomena observed in certain extreme cases of regurgitation from tricuspid deficiency, as also in 'those cases where, independently of valvular disease, there occurs an obvious blood movement in the jugular vein, with a varying state of distension of the vessel, indirectly confii-m the whole of the above position. For while a true pulse is never to be felt in the vein, an undulatory motion is seen to culminate in its greatest amount of tension, and this greatest amount of tension to be synchronous with the pulsation in the carotid artery.

Again : the ordinary explanation — that the dilatation of the ventricles is passive only, and solely caused by the forcible discharge, by the am-icles, of blood into them : or rather that it is divided into two distinct stages ; the first due to the simple elasticity of the ventricular walls, and dm'ing which stage the auricles are still dilating; the second accompanied by the systole of the auricles, in which the blood is so forcibly propelled as to dilate the ventricles strongly, — is not only inconsistent with the above view, but the structure of the auricle does not warrant such a conclusion : it has neither the general strength nor the character of fibre for the exercise of so large a power, nor does the position of the musculi-pectinati suggest it.

Without discussing what may be the motive power exercised upon the blood in its course through the veins — how much may be due to capillary force, and how much to an elastic or even to a contractile power proper to the veins themselves — I here hazard the opinion that the auricles fulfil

FUNCTION OF THE VENTRICLES.

two evident conditions : the one, in connexion with the venae cavge and pulmonaiy veins, of being the ready vessels of supply whence the ventricles, or heart proper, receive that blood which, on their expansion, they require ; the other, that of being elastic expanding vessels, and representing those enlargements wliich invariably accompany the valves of the veins, by which the tension induced by the contracting ventricles, and the sudden closing of the valves consequent on the incoming stream of blood, is compensated for. And I woidd further hazard the opinion, that any muscular power the auricles may exert on the propulsion of the blood is only secondary.

Whether the closure of the auriculo-ventricular apertures, respectively by the tricuspid and mitral valves, be due to mechanical or vital causes, probably, as it appears to me, to the former, it is not here necessary to discuss. Nor is it necessary to seek for or determine the physiological cause of the rhythmic action of the ventricle. But assuming this simpler view of the heart's action to be correct — viz., that the ventricles act, first by a process of exhaustion, and so as to suck in the blood, and then by contraction to propel it onwards— we will pass on to a consideration of the sounds, normal and diseased, thereby emitted.

CHAPTEE II.

SOUNDS OF THE JIEART.

It is generally admitted, in accordance "witli the statement of Dr. C. J. B. Williams, that the series of phenomena which are associated with each complete movement of the heart (as the impulse, sounds, pause, etc.) occupies a cycle of time, divisible into five periods ; two of these being occupied by the impulse, together with the first or systolic sound, which is dull and prolonged, the "rub" ; one by the diastolic or second sound, sharp, short, and abrupt, the " dub " ; and the remaining two by the pause. Some modern observers, however, speak of a third sound, the presystolic* (Vesal, Spring) occupying the latter half of the pause ; Pettigrew states that the sounds are really continuous, running into each other by insensible gradations. " The sounds, in fact, merge into each other precisely in the same way that the movements of the different parts of the heart merge into each other. They have their points of maximum and minimum intensity, and it is upon these the physiologist and physician fixes when he attempts to define their nature and duration."

Though adopting, as most consonant with general observation, the above division of the heart's action into five periods, yet, doubtless, very many of the hearts that one examines will warrant a division of the cycle of events into four periods only, and, in which case, the pause is diminished by one half — the first sound occupying two periods, the second sound one period, and the ^pause one period.

« Sprino- {Annales de la SocUte Medico-Chirurg. de Bruges, 1861), who refers the sounds to the contraction of the heart and valves, attribiites the presystoUc Bound to the lowering- of tlie auricido-ventricular valves.

SOUNDS OF THE HEART.

Tlie first and second sounds are now generally, if not universally, admitted to be synchronous with the closure of the valves ; the first or systolic sound with the closure of those at the auriculo-ventricular openings, the second or diastolic with the closure of the semilunar valves.

The conclusion as to the direct cause of these sounds is not so unanimous. As many as thirty different sources of the sounds of the heart have been alleged. Some writers attributing them solely and entirely to the sound emitted by the contraction of muscular fibre, and therefore due to the act of contraction in the heart itself; some to the blow of the heart on the parietes of the chest ; some to the vibration of the valves ; and some to the effect of the heart's contraction on the fluid it circulates ; and some regard these sounds as due to a combination of many of ^ these causes. My own conviction is, that the sounds referred to are mainly, if not entirely, due to the natural interference with the even flow of the blood by the various mechanisms of the heart, and that they are to be referred to the ordinary laws of hydraulics, and little, if at all, to be attributed to the contracting act of the muscle of the heart, or to any vibratory motions in the substance of the valves.

This branch of our inquiry presents itself under difficulties, and I only appfoach it with diffidence, for many of the English school, as Billing, Halford, Fuller, etc., and nearly all the writers belonging to the foreign schools, refer the sounds to the act either of muscular contractions or of valvular vibrations.

Doubtless certain sounds may, under certain circumstances, be emitted during the contractions of muscular fibre; but these sounds are neither identical nor even analogous to the audibly distinct phenomena presented during the heart's action; moreover, the intensity of the sounds emitted by the heart is not, pari passu, in accordance with the existing development of the muscular structure of the heart; on the contrary, disease in this organ, whether of hypertrophy or of attenuation, rather shows the opposite fact to be the rule.

The valves of the heart, whether considered in relation to muscular contraction or to vibration, certainly do not

SOUNDS OF THE HEART.

present x>ct se those physical conditions adequate to afford a satisfactory explanation of the production of the sounds.

These valves are not, on the one hand, muscular in tlieir structure, nor even closed through the immediate instrumentality of muscular contraction, but solely under the influence of the direct mechanical operation of hydraulic pressure; nor, on the other hand, is their size, under slow vibration, adequate to the production of so loud a sound; nor, supposing there were such adequate rapidity of viljration' is the condition of their floating in so dense a fluid, as is the blood, one thus likely to generate, or, if generated, to transmit sound.

Again, when on the closure of the several valves, the passage of the blood through their aid is not completely effected, though the valves may, and the ventricles must, contract, the former thus enjoying fuU scope for theii- vibratile qualities if they ever possessed them, and the latter for those muscular contractions which undoubtedly belong to them, the peculiar sounds said to be referable to their contractions and vibrations are no longer to be heard. It is true sounds are heard, but these are of a quaKty which cannot be referred to muscular contractions, or to membranous vibrations, though they can be, equally with the normal sounds, accounted for by hydi-aulic laws. In fact, as is so well known, a very slight distui-bance of function, or alteration in stnictui-e in these valves, so as to effect a condition either of slight obstruction, or of imperfect closure, may be sufficient to banish entirely the normal sounds, and convert them into others, very different in their character; moreover, both the normal sounds in question are emitted at the precise moment the valves have become closed, and not at the time during which the process takes place, whereby their closure is effected; while any connexion of the second soimd with the coning muscular contraction of the ventricles, or with its final energetic act, is at once set aside by the circumstance of its not being synchronous with it.