QUANTITY OF AIR RESPIRED. 



169 



The following table expresses the result of numerous exper- 

 iments by Mr. Hutchinson on this subject, the instrument used 

 to gauge the inspiratory and expiratory power being a hsema- 

 dynamometer (see p. 138), to which was attached a tube fitting 

 the nostrils, and through which the inspiratory or expiratory 

 eifort was made : 



Mr. Hutchinson remarks : " Suppose a man to lift by his 

 inspiratory muscles three inches of mercury, what muscular 

 effort has he used ? The mere quantity of fluid lifted may be 

 very inconsiderable (and as such 1 have found men wonder 

 they could not elevate more), but not so the power exerted, 

 when we recollect that hydrostatic law, which Mr. Bramah 

 adopted to the construction of a very convenient press. To 

 apply this law here, the diaphragm alone must act under such 

 an effort, with a force equal to the weight of a column of mer- 

 cury 3 inches in height, and whose base is commensurate to 

 the area of the diaphragm. The area of the base of one of 

 the chests now before the Society, is 57 square inches ; there- 

 fore, had this man raised 3 inches of mercury by his inspira- 

 tory muscles, his diaphragm alone in this act must have op- 

 posed a resistance equal to more than 23 ounces on every inch 

 of that muscle, and a total weight of more than 83 pounds. 

 Moreover, the sides of his chest would resist a pressure from 

 the atmosphere equal to the weight of a covering of mercury 

 three inches in thickness, or more than 23 ounces on every 

 inch surface, which, if we take at 318 square inches, the chest 

 will be found resisting a pressure of 731 pounds; and allowing 

 the elastic resistance of the ribs as 1^ inch of mercury, this 

 will bring the weight resisted by the chest, as follows : 



Diaphragm, 

 Walls of the chest, 

 Elastic force, . 



83 Ibs. 

 731 " 

 232 " 



Total, 1046 



"In round numbers it may be said, that the parietes of the 



