1050 



THORAX. 



These facts show that we should be guarded 

 in determining the living respiratory move- 

 ments by experiments upon the dead subject. 



It should be constantly borne in mind, that 

 to increase or diminish an intercostal space is to 

 elevate or depress the ribs, and that to elevate 

 or depress the ribs is to increase or diminish 

 their intercostal spaces : the one cannot be 

 accomplished without the other. Some au- 

 thors have spoken of these as distinct ; thus, 

 that in inspiration the superior ribs ap- 

 proximate each other, whilst they are raised, 

 or that their rising or falling does not neces- 

 sarily involve an increase or diminishing of 

 the intercostal spaces ; but these two changes 

 are simultaneous and cannot be done sepa- 

 rately. 



2nd. TJie effect of tensions, oblique, perpen- 

 dicular, and decussating, between the moveable 

 levers or ribs. We employ a strip of vul- 

 canised Indian- rubber for a force representing 

 muscular contraction. A strip of this sub- 

 stance, of uniform thickness, \ of an inch 

 broad and 10 inches long, increased its length, 

 with an increasing weight, as follows : 



Fig. 686. 



Weight 



in 

 ounces. 



2 



4 



8 



16 



32 



64 



the pan holding the 

 weight = 850gr. = 



do. 

 do. 

 do. 

 do. 

 do. 

 do. 



= 1725 



= 2600 

 = 4350 

 = 7850 

 = 14850 

 = 28850 



Increased 

 length of 

 Indian 

 rubber, 

 gr. inches. 



a 



1287^ 



I 



H 



4 



Although not exactly in accordance with 

 the law of perfect elasticity, yet it is roughly 

 so and enough for our purpose, viz. the 

 tension is greatest when most stretched, and 

 weakest when least stretched, corresponding 

 with muscular contraction. 



Let E E (Jig. 686.) be fixed, A B and c i>two 

 moveable bars as before, t an oblique tension ; 

 if t shortens, it has been supposed that the two 

 bars would assume the position of A B' and 

 c D ; but not so : they both rise like A B" and 

 c D" until the two bars touch each other.* If 

 we prevent this touching of the two bars by 

 a rigid link, like that on parallel rulers, placed 

 as at s fig. 687., then the tension will still 

 raise the bars to o o'. In this experiment 

 three circumstances may be noticed. 1st, 

 that the bars have been elevated ; 2dly, that 

 the perpendicular distance between them has 

 been diminished ; and 3dly, that the tension 

 t has been shortened in attaining the position 

 o o'. Place the tension in a contrary direc- 

 tion, as between the bars A' B' and c' D', and 

 the bars are brought into a contrary position, 

 drawn downwards to o' o'". This can be 



* This appears to have been known to Hamberger ; 

 but the author of this article was not aware of it 

 until four years after he first introduced this move- 

 ment to notice. (See Med. Chirurg. Trans, vol. 29, 

 p. 213.) It is certain that Hamberger's views were 

 not taught in any physiological school in this coun- 

 try, Germany, or France, nor noticed in any of our 

 philosophical works. 



A 



Effect of oblique tension on separate bars. 



demonstrated by a model, using a spring or 

 Indian-rubber as the tension, and may be 



Fig. 687. 



explained as follows. Let A B, fig. 688., repre- 

 sent one bar, c D the perpendicular fixed body ; 

 B is the free extremity of the bar ; K an 

 axis from which a parallel bar has been re- 

 moved. Let e, i, and o be other fixed points ; 

 connect e to B by an elastic tension, and the 

 bar B will be moved towards e. Let the ten- 

 sion be fixed at i or o, still the bar B will be 

 raised towards the respective points. Let 

 the tension be fixed at K (the centre of mo- 

 tion of the bar which we suppose is removed), 

 and still the bar A B will be raised upwards 

 towards K, and assume the position of A B, 

 K L (fig. 689.) at M. But it is not necessary to 

 this that the elastic force should extend from 



