1066 



THORAX. 



anteriorly, left white, the reserve volume, 

 or latitude of movement appropriated for dis- 

 placing that air left in the lungs at the 

 end of an ordinary expiration ; the black 

 stripe next anteriorly represents the mobi- 

 lity for commanding the volume of breathing 

 air; and lastly, beyond this another white 

 stripe shows the extreme limit of inspiration 

 or thoracic mobility commanding the com- 

 plemental volume of air. These last three 

 viz. the complemental, breathing, and reserve 

 volumes conjointly we style vital capacity. 

 The absolute capacity may be considered as all 

 the divisions combined in one. 



Whatever limits the mobility of the thorax 

 must modify the volume of air respired. 

 This applies to any or all of the above 

 movements. Therefore the measure of the 

 volume of air displaced becomes a measure 

 of the thoracic mobility ; and as disease affects 

 the mobility of the chest, the measure of the 

 volume of respired air becomes a measure of 

 disease. 



The residual volume is entirely independ- 

 ent of the will, and always present in the 

 chest. The reserve volume, to use a simile, 

 is a " tenant at will." The breathing volume 

 is constantly passing out and in, many times 

 a minute. The complemental volume is seldom 

 in the chest, and then only for a very brief 

 period. 



Whatever be the breathing volume ne- 

 cessary for our well-being, the mobility 

 demanded to maintain it is an intermediate 

 mobility, just as the dark stripe inJZg. 703. is 

 intermediate between the white stripes ; so 

 that at both ends of the ordinary breathing 

 mobility there exists a spare mobility, which 

 we can command into action according to the 

 necessities required. This reserve and com- 

 plemental mobility may be looked upon as 

 a broad, spare margin which encompasses 

 our breathing ; so that any sudden exertion 

 may not (as it otherwise would) produce 

 painful dyspnoea and premature death. 



This spare mobility, therefore, is always 

 ready to admit of irregularities in the ordinary 

 breathing, such as frequent or infrequent, quick 

 or slow, regular or irregular, great or small, 

 equal or unequal, easy or difficult, complete or 

 incomplete, long or short, abdominal or costal; 

 as in coughing, running, laughing, crying, sing- 

 ing, sighing, and vociferating, many of which 

 are but extensions or modifications of the or- 

 dinary mobility, infringing upon this margin 

 the complemental or reserved mobility. 



This spare mobility is not only ready for 

 such exigencies as above mentioned, but it 

 becomes a reservoir for " times of need." 

 Thus a man can take from 230 to 300 cubic 

 inches of fresh air into his lungs, and live upon 

 it without inconvenience for two minutes with- 

 out breathing. * The knowledge of this fact 



* It is better to inspire and expire forcibly five 

 or six times, cleansing the lungs of the old air, and 

 then give one deep inspiration, and there hold. 

 For the first 15 seconds a giddiness will be ex- 

 perienced ; but when this leaves us, we feel not the 



would be of much use towards rescuing 

 a fellow creature from suffering amidst dense 

 smoke or in an irrespirable atmosphere, 

 as is found sometimes in mines and wells. 

 A variation of this condition was once wit- 

 nessed when Mr. Brunei descended to ex- 

 amine the breach which the river had made 

 in the Thames Tunnel. Having lowered 

 the diving-bell nearly 30 feet to the mouth of 

 the opening, this was found too narrow to 

 admit the bell ; so that no further observation 

 could be made upon the workings, which were 

 about 8 feet or 10 feet deeper: Mr. Brunei, 

 therefore, laying hold of a rope, left the bell, 

 and dived himself down the opening. His 

 companions in the bell, being alarmed at the 

 length of his stay, now about two minutes, 

 gave the signal for pulling up ; and the diver, 

 unprepared for the signal, had hardly time to 

 catch the rope, which he had let go, and was 

 surprised to find, on coining into the bell, 

 that he had remained below so long. On 

 descending again, he found that he could with 

 ease remain fully two minutes under water. In 

 this case the atmosphere, under a pressure of 

 30 feet of water, charged the lungs with nearly 

 a double volume of air compressed into the 

 same bulk as one volume at the surface of 

 the water. Our ordinary breathing volume 

 can only supply us for from three to five 

 seconds ; for if we suddenly stop breathing 

 for that time, we experience a degree of 

 inconvenience. 



Of the volumes of air expelled from the 

 . A knowledge of this is of incalcu- 

 lable value to the physician and to the surgeon ; 

 for disease cannot attack the lungs or the 

 thoracic boundaries, without diminishing the 

 respiratory volume, which change ultimately 

 leads to the variations of the respiratory 

 murmurs, first noticed as a diagnostic sign of 

 disease by Laennec. Many experimenters 

 have measured the different volumes of re- 

 spired air, not primarily in reference to 

 disease, but merely as collateral to the ob~ 

 servations of the chemist : hence experiments 

 have been few, and deductions highly dis- 

 crepant. 



(a) Residual volume. Dr. Hales notices this 

 volume, but assigns no measure for it*$ 

 Allen and Pepys estimate it at 108 cubic 

 inches in stout men of 5 feet 10 inches f; 

 Davy at 41 cubic inches J ; Goodwyn, by 

 the mean of seven experiments, at 108 cubic 

 inches; Kite, who writes expressly upon 

 submersion, is obscure upon this point ; 

 Dr. Bostock allows 120 cubic inches || ; 

 Dunglison gives Menzie's estimate of 179 

 cubic inches ; Jurin estimates it at 220 cubic 

 inches ; Fontana at 40; and Cuvier at from 



slightest inconvenience for want of air; and two 

 minutes of time can be passed through without 

 breathing. The most expert pearl-divers cannot re- 

 main under water for a longer time. 



* Stat, vol. i., p. 239. 



f Phil. Tr., 1809., vol. xcix. pp. 404 428. 



I Chem. and Phil. Remarks, p. 410. 



Essays and Obs. Physical and Med. 1795, p. 8. 



|| E . Phvs. 3d. Ed. p. 318. 



