Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 2: Dia-Ins
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25760/622/
614 
HEART. 
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.}; 2dly. 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 the 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. 
In 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 hy the 
application of a stimulant, wre were convinced that 
contraction of the auricle, when excited by stimu¬ 
lation applied to itself alone, was 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 heart’s 
action occurred after the contraction of the auri¬ 
cles. 
contractions of the ventricles do not neces¬ 
sarily follow those of the auricles, unless 
the contractions of the auricles occasion the 
application of a stimulaut to the inner sur¬ 
face of the ventricles sufficient to excite them 
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 drinking, 
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 rhythm 
of the heart. As the dull prolonged sound is 
synchronous with the impulse of the heart, 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 
systole of the auricles ; and to this he was 
naturally led by the supposition that their con¬ 
traction must also produce some sound. From 
the weight of Laennec’s authority, this opinion 
* Op. cit. cap. v.
        

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