294 



NATURAL HISTORY OF ORGANIZED BODIES. 



clastic pouch with a certain force, tends to escape outwards by driving back the 

 thin membrane which confines it ; this it effects at the sole point where the walls 

 offer little resistance. Suppose, for an instant, that, in place of the thin mem- 

 brane which now forms the hernia, there were a spongy but more consistent 

 tissue, like that of the lungs ; the hernia would become strangulated between 

 the edges of the opening and be unable to re-enter spontaneously, even when 

 tlie effort has ceased. Many other demonstrations might be made by means of 

 this simple apparatus. 



Without digressing from the subject, another fact may be noticed which long 

 seemed obscure, but which is susceptible of a synthetic demonstration at once 

 simple and convincing. Have the intercostal muscles any action on the move- 

 ment of the ribs, and, if so, what is that action? This was the subject of much 

 discussion among the physiologists of the last centtuy. 



The solution of the question was demanded of experiment, and it was found 

 that, in living animals, the external intercostal muscles contract at every inspi- 

 ration of air. But this result of observation presented something paradoxical 

 and inexplicable. The external intercostals are extended between two ribs : 

 it Avould seem, therefore, that they ought, in contracting, to bring the ribs nearer 

 to one another. Now, at the moment of inhalation, the ribs separate and the 

 intercostal spaces are enlarged. 



P. Berard, in his courses of physiology at the Faculty of Medicine, was 

 accustomed to recall the discussions in question, and removed any hesitation on 

 the part of his auditory by tracing on a tablet a schematic figure which rendered 

 the phenomenon easily intelligible. He would state, at the same time, that he 

 had received from Dr. Hutchinson a small apparatus formed of pieces of wood 

 in imitation of the arrangement of the ribs in relation to the vertebral column, 

 and of elastic bandelets which represented the action of the external intercostal 

 muscles. The whole, when the parts representing ribs were lowered so as to 

 exert a traction upon the elastic bandelets, was calculated to take the position 

 attending the act of inhalation in the animal frame. Annexed is an apparatus 

 which 1 have constructed upon these indi- 

 cations and which aptly reproduces the phe- ] '\ 

 nomenon in question, {Fig. 2.) 



The vertebral column is represented l\y a 

 piece of vertical wood on which three trans- 

 verse pieces are articulated : these represent i — 

 the ribs. The direction of the intercostal ^ — 

 muscles is indicated by that of the braces of 



caoutchouc fastened by pins on the cross- i 



bars of wood. When the ribs are horizon- I 



tal, as in the figure, there is a considerable 



interval between them, but the insertions, | 



A, B, of the brace of caoutchouc are not so I 



widely separated as in the case when the rib- 

 pieces, being lowered, approach and touch 

 one another. In that case, the brace of 

 caoutchouc corresponds to the diagonal of a 

 very oblique parallelogram. Now, the 

 position of the elastic brace is that which 

 the external intercostals present in relation 

 to the ribs. The contraction of these mus- 

 cles serves, therefore, to raise the ribs, as '/, / 

 the elasticity of the caoutchouc acts in the / ^ / 

 schema which we have been describing. / '' .•'' 



Mcf^t 



