170 RESPIRATION. 



thorax resisted 1000 Ibs. of atmospheric pressure, and that not 

 counterbalanced, to say nothing of the elastic power of the 

 lungs, which co-operated with this pressure. 



" I would not venture at present to state exactly the distri- 

 bution of muscular fibre over the thorax, which is called into 

 action when resisting this 1046 Ibs., but I think I am safe in 

 stating that nine-tenths of the thoracic surface conspire to 

 this act. 



" What is here said of the muscular part of the chest resist- 

 ing such a force, must not be confounded with a former state- 

 ment of 'two-thirds being lifted by the inspiratory muscles, and 

 one-third left dormant,' under a force equal to 301 Ibs. In 

 this case the 301 Ibs. are lifted; in the other, nine-tenths of 

 1046 Ibs. are said to be resisted. 



" The glass receiver of an air-pump may resist 15 Ibs. on the 

 square inch, yet it may be said to lift nothing. This question 

 of the thoracic muscular force and resistance, and muscular 

 distribution, is rendered complicate by the presence of so much 

 osseous matter entering into the composition of the chest, which 

 can scarcely be considered to act the same as muscle." 



The great force of the iuspiratory efforts during apnoea was 

 well shown in some of the experiments performed by the Medico- 

 chirurgical Society's Committee on Suspended Animation. On 

 inserting a glass tube into the trachea of a dog, and immersing 

 the other end of the tube in a vessel of mercury, the respiratory 

 efforts during apnoea were so great as to draw the mercury four 

 inches up the tube. The influence of the same force was shown 

 in other experiments, in which the heads of animals were im- 

 mersed both in mercury and in liquid plaster of paris. In both 

 cases the material was found, after death, to have been drawn 

 up into all the bronchial tubes, filling the tissue of the lungs. 



Much of the force exerted in inspiration is employed in over- 

 coming the resistance offered by the elasticity of the walls of 

 the chest and of the lungs. Mr. Hutchinson estimated the 

 amount of this elastic resistance, by observing the elevation of 

 a column of mercury raised by the return of air forced, after 

 death, into the lungs, in quantity equal to the known capacity 

 of respiration during life ; and he calculated that, in a man 

 capable of breathing 200 cubic inches of air, the muscular 

 power expended upon the elasticity of the walls of the chest, 

 in making the deepest inspiration, would be equal to the rais- 

 ing of at least 301 pounds avoirdupois. To this mus-t be added 

 about 150 Ibs. for the elastic resistance of the lungs themselves, 

 so that the total force to be overcome by the muscles in the 

 act of inspiring 200 cubic inches of air is more than 450 Ibs. 



In tranquil respiration, supposing the amount of breathing 



