Licence: Public Domain Mark
Credit: Heart / by John Reid. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![contraction of the auricle must force an ad- ditional quantity into the ventricle, and this, though small in quantity, may be quite suffi- cient to excite the ventricles to contraction, when the irritability is not too much impaired.* It is only in this manner, taken along with the greater irritability of the internal surface over the external, that we can explain the observa- tion made by Dr. Knox in the course of his experiments upon the irritability of the heart in fishes, where, when the irritability was nearly exhausted, contractions excited in the auricle ■were sometimes followed by contractions of the ventricle, when irritation of the outer surface of the ventricle itself produced no effect.f Cer- tainly, under ordinary circumstances, this regu- larity of the heart, so necessary for the proper performance of its functions, is a marked fea- ture in its action ; but that it is not either ne- cessarily connected with its structure or vital properties, but depends solely on the manner in which its stimulant, the blood, is applied, is proved by various facts. 1st. The movements of the auricles and ventricles generally cease at different times after death; and though the auricles much more frequently continue to con- tract after the ventricles, yet several accurate experimenters have observed the left auricle become quiescent before its corresponding ventricle.]: 'idly. When the movements of the ventricle have ceased, while the auricles continue to contract, the ventricle may generally be excited to vigorous contractions by the ap- plication of a powerful stimulus. 3dly. When the irritability of the heart becomes somewhat languid, two, three, or sometimes six or seven contractions of the auricle may take place be- fore the ventricles are roused to contraction; the evident deduction from which is, that the * When ihe heart has ceased to contract, it may frequently be called into pretty vigorous action by opening one of the large veins, and blowing some air into its cavities. t I have repeatedly attempted to ascertain if the circumstances here described as sometimes occurring in the cold-blooded animals could be observed in the warm-blooded animals, but without success. Id one experiment upon the heart of a rabbit, after all the movements of the ventricles had ceased, but where they could still he readily excited by the application of a stimulant, we were convinced that contraction of the auricle, when excited by stimu- lation applied to itself alone, whs sometimes fol- lowed by contaction of the ventricle even after the ventricle had been slit open. But in subsequent experiments upon dogs, we ascertained a source of fallacy which we had overlooked in the other expe- riment, for we found that a slight movement of the heart on the surface upon which it rests, such as that caused by a very gentle pull at the large arteries, and not exceeding the effects produced by the contraction of the auricle, was, in some of these cases, sufficient to excite contractions of the ventricles. \ In one experiment upon a cat, I distinctly ob- served the right ventricle occasionally pulsate twice for each pulsation of the auricle. In another experiment, 1 distinctly observed the contractions of the ventricles precede those of the auricles, •when the contractility of the heart had become en- feebled. In this case, the pause in the hearths action occurred after the contraction of the auri- contractions of the ventricles do not hkos- sarily follow those of the auricles, unless liie contractions of the auricles occasion the application of a stimulant to the inner sur- face of the ventricles sufficient to excite lliem to contraction. 4thly. The movements of the ventricles and auricles will go on in the same manner, though detached from each other by the knife. 5thly. If we were allowed to argue from final causes in negative cases, we could easily shew that a peculiar endow- ment, such as we are contending against, would not be of the slightest advantage in se- curing the regularity and constancy of the heart's movements. It appears, then, quite un- philosophical to call in the agency of some un- known and indefinite principle for the produc- tion of these periodic movements, as they have been called, of the different chambers of the heart, when they can be satisfactorily referred to the laws which regulate muscular contracti- lity in other parts of the body. We have here a beautiful example of the manner in which nature produces adaptation of means to an end, not by the creation of new properties, which we, in our ignorance, sometimes erroneously attribute to her, but by the employment of those already in use in the performance of other functions, only modified to accommodate them to the circumstances under which they are placed. Sounds of the heart.—On applying the ear over the region of the heart, two distinct sounds are heard accompanying its contraction. Though the existence of such sounds seems to have been known to Harvey,* who compares them to the noise made by the passage of fluids along the oesophagus of a horse when drinkmg, yet, as is well known, it is to Laennec that we owe the first accurate description of the charac- ter of these sounds, the order of their succes- sion, and the manner in which they may here- after be made available for the important pur- poses of the diagnosis of the diseases of the heart. The first of these sounds is dull and pro- longed ; the second, which follows closely upon the first, is sharp and quick, and is likened by Laennec to the flapping of a valve, or the lap- ping of a dog. After the second sound a pause ensues, at the end of which the sounds are again heard. These three—the first sound, the second sound, and the pause—occur in the same uniform order, and when included along with the movements of the heart, to which they owe their origin, have received the term rhi/thm of the heart. As the dull prolonged sound is synchronous wilii the impulse of the lieart, and consequently with the contraction of its ventri- cles, Laennec attributed this sound to the con- traction of the ventricles. The second sound, which is synchronous with the diastole of the ventricles, he supposed must depend upon the svstole of the auricles ; and to this he was naturally led by the supposition that their con- tractionmust also produce some sound. From the weight of Laennec's authority, this opinion](https://iiif.wellcomecollection.org/image/b21908503_0042.jp2/full/800%2C/0/default.jpg)
