RESPIRATORY RHYTHMIC MOVEMENTS IN ANIMALS 273 



with a movable partition (the mitral valve) between them. The thorax may be taken to represent the left am-icle, 

 the abdomen the left ventricle, and the diaphragm the mitral valve. The cardiac muscular movements and respira- 

 tory movements are rhythmical and alternating ; the one cavity opening when the other is closing and vice versd. 

 Thus in the chest the thoracic cavity opens when the abdominal cavity closes, and the converse. These diametrically 

 opposite movements in the thorax and abdomen occur simultaneously. In both the opening and closing move- 

 ments the diaphragm plays an important part. Thus it descends when the thorax opens, and ascends when it closes. 

 It in this way alternately increases and decreases the capacity of both cavities. The mitral valve of the left 

 ventricle in like manner descends and ascends and alternately increases and diminishes the size of the left auricle 

 and ventricle. The movements of the diaphragm are rhythmic, and accurately adapted to those of the chest 

 and abdomen. 



The glottis, situated within the larynx, also takes part in the rhythmic respiratory movements. From this it 

 will be seen that there are four different rhythmic movements connected with respiration in animals, namely, those 

 of the glottis, chest, abdomen, and diaphragm. The respiratory movements, although apparently simple, are highly 

 complex. They have unfortunately never received the attention they deserved. It is therefore fitting that in 

 the present section I should describe the respiratory rhythms somewhat in detail, illustrating what I have to say 

 by carefully selected figures. I consequently, in this connection, give views of the lungs, the larynx, the bronchial 

 tubes, the glottis, the bones and cartilages of the chest, the thoracic and abdominal muscles (esfecially the recti 

 abdominis), the diaphragm, the appearance presented by the body in inspiration and expiration, &c. 



Much of the confusion connected with the respiratory rhythmic movements is traceable to authors failing to 

 grasp the fact that the several rhythms occurring in the glottis, chest, abdomen, and diaphragm are only parts of 

 one great rhythm which may be aptly designated the respiratory rhythm. The confusion is also partly due to 

 anatomists assigning separate movements to individual muscles which can only act in groups or as wholes. As it is 

 not possible to define the action of the muscles in any part of the heart, neither is it possible to defme with adequate 

 precision the action of separate muscles in any part of the chest, abdomen, and diaphragm. The chest, abdomen, 

 and diaphragm exercise opening or centrifugal, and closing or centripetal movements precisely analogous to those 

 witnessed ia the heart. Lastly, physiologists have never fully reaHsed the inherent nature of the rhythmic respira- 

 tory movements, and have referred them directly or indirectly to irritabiUty and extraneous stimulation. They have 

 overlooked the fact that the rhythmic movements are fundamental, spontaneous, and independent — the one move- 

 ment never causing the other ; that the opening centrifugal and the closing centripetal movements are both vital in 

 character, and that elasticity plays quite a subordinate part in respiration. At present there is a prevailing behef 

 that the several compartments of the heart are closed by vital acts ; the opening of the compartments being largely 

 due to the elasticity of the muscles which act passively. 



Similarly but conversely, the chest is said to be opened by vital movements, the closure being effected passively 

 by the resihency and elasticity of the muscles and ribs. 



Why, one naturally inquires, should the heart be closed by vital movements and the chest opened by them ? 

 The contradiction here pointed out demoUshes the prevailing theory of muscular action not only in the hollow 

 viscera, but also in the voluntary muscles. The opening and closing of the hollow muscles forming the viscera, 

 and the contraction and relaxation of the voluntary muscles, can only be performed by independent vital acts : 

 mere elasticity cannot be said to influence the action of muscles to any appreciable extent. Up till the present 

 the causes of the rhythmic movements, particularly the respiratory ones, have remained a close secret. 



A curious point to be noted in connection with rhythmic movements is this. They occur in the protoplasm 

 of plants and in both kinds of muscles, namely, the pale or unstriated involuntary muscles and the red or striated 

 voluntary muscles of animals. 



The explanation is that, strictly speaking, no real distinction (the power of the will over the voluntary muscles 

 excepted) can be drawn between the involuntary and voluntary muscles, either structurally or functionally. The 

 one runs into the other. The voluntary muscle, as I showed in 1872,^ is a higher development or differentiation of 

 the involuntary muscle, and it can be made to act either with or without the aid of intelKgence. A pedestrian 

 can walk either automatically or intelligently, and a clever pianist can perform the most difficult music and keep 

 up a conversation altogether disregarding the movements of the fingers engaged. A lunatic not unfrequently sets 

 up rhythms in his limbs or other parts of his body, and produces a series of grotesque see-saw movements which 

 he continues for hours. 



The weaving movements of animals are to be placed in the same category. Some people known to me slowly 

 flex and extend their inferior extremities during sleep. In all cases where the voluntary muscles act involuntarily 



' "The Physiology of the Circulation in Plants, in the Lower Animals, and in Man." Edinburgh Medical Journal, 1872, 187-3. Also 

 separate volume published 1874 by Macmillan with 250 woodcuts (see pp. 208-214). 



VOL. I. ' 2 M 



