GENERAL STRUCTURE OF THE RESPIRATORY ORGANS. 373 



indicated, and the total pressure over the surface of the chest, reckoning its 

 area at 206 square inches: 



Cubic inches. Pressure in bright Pressure Total 



of Mercury. per sq. in. pressure. 



Air forced in 70, Resisting elasticity, 1.00 inch. 7 8 oz. 104.4 Ibs. 



" HO, " " 1.50 " 11.7 " 1506 " 



" 180, " " 3.25 " 25.3 " 326.3 " 



" 200, " " 4 50 " 35.1 " 451.9 " 



To this 451.9 Ibs. must be added at least 128 Ibs. for the elastic force of the 

 lungs themselves at that degree of distension, making altogether .580 Ibs. ; 

 and as the subject of this observation could expire during life considerably 

 more air than the highest amount forced into his chest after death, there 

 can be little doubt (judging from the rapid ratio in which the elastic force 

 increases when the distension is approaching its limits) that the muscular 

 power required to overcome this, towards the close of a very deep inspira- 

 tion, could not have been less than 1000 Ibs. The co-operation of the elas- 

 tic resistance with the expiratory movement, and its antagonism to the in- 

 spiratory, is doubtless the principal cause why the power of the expiratory 

 muscles, as tested by the height of the column of mercury supported by the 

 air, should always be greater than that of the iuspiratory muscles ; J and why 

 the expiratory power should be very much greater when the chest has been 

 well filled with air, than when it is comparatively empty. The following is 

 given by Dr. Hutchiuson as the range through which these powers may vary 

 within the limits of health : 



Power of Power of 



Inspiratory Muscles. Expiratory Muscles. 



1.5 inch, Weak, 2 inches. 



20" Ordinary, 25" 



4.5 " Remarkable, . . . 5.8 " 



7.0 " Very extraordinary, . . . 10.0 " 



The expiratory power may be augmented by the habitual performance of 

 movements in which they participate; and thus the inspiratory power is the 

 preferable test of the vis vitce. This has been found by Dr. Hutchinson to 

 bear some relation to height, being greatest (on an average of a considerable 

 number of cases) when the stature is 5 feet 7 or 8 inches; and diminishing 

 above that height, as well as below it. Fick estimates that the, work ac- 

 complished in effecting the inspiration of 600 c.c. is equivalent to 0.63 kilo- 

 grammetre, and Prof, flaughton estimates the daily work of the respiratory 

 muscles at 21 foot-tons.' 2 



292. It is impossible to form a correct estimate, by observations on one's- 

 self, of the usual number and extent of the respiratory movements ; since 

 the direction of the attention to them is certain to increase their frequency 

 and amount. In general it may be stated, that from 16 to 20 alternations 

 usually occur in a minute; 3 of these, the ordinary inspirations involve but 

 little movement of the thorax ; but a greater exertion is made at about every 

 fifth recurrence. According to Quetelet, the infant breathes 



' See Dr. Hutchinson, op. cit, p. 1061. 



2 Lecture delivered at the Meeting of Brit. Med. Assoc. at Oxford, August, 1868. 



3 See Dr. Hutchinson's Table, in Cyclop, of Anat. and Phys , vol. iv, p. 1085. 



