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RESPIRATORY RHYTHMIC MOVEMENTS IN ANIMALS 273<br />
with a movable partition (the mitral valve) between them. The thorax may be taken to represent the left am-icle,<br />
the abdomen the left ventricle, and the diaphragm the mitral valve. The cardiac muscular movements and respira-<br />
tory movements are rhythmical and alternating ; the one cavity opening when the other is closing and vice versd.<br />
Thus in the chest the thoracic cavity opens when the abdominal cavity closes, and the converse. These diametrically<br />
opposite movements in the thorax and abdomen occur simultaneously. In both the opening and closing move-<br />
ments the diaphragm plays an important part. Thus it descends when the thorax opens, and ascends when it closes.<br />
It in this way alternately increases and decreases the capacity of both cavities. The mitral valve of the left<br />
ventricle in like manner descends and ascends and alternately increases and diminishes the size of the left auricle<br />
and ventricle. The movements of the diaphragm are rhythmic, and accurately adapted to those of the chest<br />
and abdomen.<br />
The glottis, situated within the larynx, also takes part in the rhythmic respiratory movements. From this it<br />
will be seen that there are four different rhythmic movements connected with respiration in animals, namely, those<br />
of the glottis, chest, abdomen, and diaphragm. The respiratory movements, although apparently simple, are highly<br />
complex. They have unfortunately never received the attention they deserved. It is therefore fitting that in<br />
the present section I should describe the respiratory rhythms somewhat in detail, illustrating what I have to say<br />
by carefully selected figures. I consequently, in this connection, give views of the lungs, the larynx, the bronchial<br />
tubes, the glottis, the bones and cartilages of the chest, the thoracic and abdominal muscles (esfecially the recti<br />
abdominis), the diaphragm, the appearance presented by the body in inspiration and expiration, &c.<br />
Much of the confusion connected with the respiratory rhythmic movements is traceable to authors failing to<br />
grasp the fact that the several rhythms occurring in the glottis, chest, abdomen, and diaphragm are only parts of<br />
one great rhythm which may be aptly designated the respiratory rhythm. The confusion is also partly due to<br />
anatomists assigning separate movements to individual muscles which can only act in groups or as wholes. As it is<br />
not possible to define the action of the muscles in any part of the heart, neither is it possible to defme with adequate<br />
precision the action of separate muscles in any part of the chest, abdomen, and diaphragm. The chest, abdomen,<br />
and diaphragm exercise opening or centrifugal, and closing or centripetal movements precisely analogous to those<br />
witnessed ia the heart. Lastly, physiologists have never fully reaHsed the inherent nature of the rhythmic respira-<br />
tory movements, and have referred them directly or indirectly to irritabiUty and extraneous stimulation. They have<br />
overlooked the fact that the rhythmic movements are fundamental, spontaneous, and independent—the one move-<br />
ment never causing the other ;<br />
that the opening centrifugal and the closing centripetal movements are both vital in<br />
character, and that elasticity plays quite a subordinate part in respiration. At present there is a prevailing behef<br />
that the several compartments of the heart are closed by vital acts ;<br />
due to the elasticity of the muscles which act passively.<br />
the opening of the compartments being largely<br />
Similarly but conversely, the chest is said to be opened by vital movements, the closure being effected passively<br />
by the resihency and elasticity of the muscles and ribs.<br />
Why, one naturally inquires, should the heart be closed by vital movements and the chest opened by them ?<br />
The contradiction here pointed out demoUshes the prevailing theory of muscular action not only in the hollow<br />
viscera, but also in the voluntary muscles. The opening and closing of the hollow muscles forming the viscera,<br />
and the contraction and relaxation of the voluntary muscles, can only be performed by independent vital acts :<br />
mere elasticity cannot be said to influence the action of muscles to any appreciable extent. Up till the present<br />
the causes of the rhythmic movements, particularly the respiratory ones, have remained a close secret.<br />
A curious point to be noted in connection with rhythmic movements is this. They occur in the protoplasm<br />
of plants and in both kinds of muscles, namely, the pale or unstriated involuntary muscles and the red or striated<br />
voluntary muscles of animals.<br />
The explanation is that, strictly speaking, no real distinction (the power of the will over the voluntary muscles<br />
excepted) can be drawn between the involuntary and voluntary muscles, either structurally or functionally. The<br />
one runs into the other. The voluntary muscle, as I showed in 1872,^ is a higher development or differentiation of<br />
the involuntary muscle, and it can be made to act either with or without the aid of intelKgence. A pedestrian<br />
can walk either automatically or intelligently, and a clever pianist can perform the most difficult music and keep<br />
up a conversation altogether disregarding the movements of the fingers engaged. A lunatic not unfrequently sets<br />
up rhythms in his limbs or other parts of his body, and produces a series of grotesque see-saw movements which<br />
he continues for hours.<br />
The weaving movements of animals are to be placed in the same category. Some people known to me slowly<br />
flex and extend their inferior extremities during sleep. In all cases where the voluntary muscles act involuntarily<br />
' "The Physiology of the Circulation in Plants, in the Lower Animals, and in Man." Edinburgh Medical Journal, 1872, 187-3. Also<br />
separate volume published 1874 by Macmillan with 250 woodcuts (see pp. 208-214).<br />
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VOL. I.<br />
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