for restoring the Action of the Lungs. 279 
¢¢ 4, The blood derives heat from tiie decomposition of the in- 
~spired air; all the latent heat of the oxygen -gas not being ne- 
-eessary to the formation of carbonic acid gas. 
«© 5, The dark colour of the venous blood is owing to its be- 
ing surcharged with carbon, and the bright scarlet colour of 
the arterial Llood, to its parting with carbon in the process of 
breathing.” 
It may be added, that the volume of the newly formed carbonic 
acid gas amounts to 44 to 8 per cent. of the whole elastic mass, 
which, however, is modified by circumstances, as Dr. Prout has 
shown: the quantity of carbonic acid gas is diminished, for in- 
stance, when mercury or spirits have been used. ; 
It is computed that an ordinary person consumes about 46,000 
cubic inches of oxygen per diem, and that there are 20 respira- 
tions every minute. 
By far the most interesting remarks on the elasticity of the 
lungs, and mechanism of respiration, are contained in an excellent 
-paper by Dr. Carson, published in the Transactions of the Royal 
Society for 1820, Part I. page 29, &c. 
This ingenious author found that a column of water of 1! foot 
high, was not a counterpart to the resilience of the lungs of an 
ox at their usual dilation. In calves, sheep, and large dogs, this 
elasticity is estimated by the pressure of a column of water from 
1 to 14 foot high; and in rabbits and cats, as counterbalanced 
_.by 6 to 10 inches of water. 
Breathing, therefore, Dr. Carson very properly ascribes to an 
interminable combat between the resilience of the lungs and the 
irritability of the muscular fibre of the diaphragm. We have here 
displayed to us a simple but beautiful machinery, “ by which the 
heart and diaphragm, and perhaps various other organs, are as 
necessarily and as effectively influenced as the piston of the steam- 
-engine by the expansive powers of steam.” 
** Two powers,”’ adds Dr. C., * are therefore concerned in re- 
 gulating the movements, and in varying the dimensions and form 
of the diaphragm ; the elasticity of the lungs, and the contractile 
power of the muscular fibres of the diaphragin. Of these powers, 
the one is permanent and equable; the other, variable, and exerted 
at intervals. The contractile power of the diaphragm, when fully 
exerted, is evidently much stronger than its antagonist the resi- 
lience of the lungs; but the latter, not being subject to exhaustion, 
takes advantage of the necessary relaxations of the former, and, 
rebounding like the stone of Sisyphus, recovers its lost ground, 
and renews the toil of its more powerful opponent.” 
Thus has Dr, Carson given us a most interesting account of 
one of the most important organs of the vital frame. It bears 
the signet of experiment, and has in its features much that looks 
like 
