412 ON RESPIRATION. 



it seems evident, from the analogous phenomenon of the excretion of turpen- 

 tine, camphor, alcohol, and other odorous substances, which have been intro- 

 duced into the venous system, either by natural absorption, or by direct injection ; 

 and also from the suddenness with which it manifests itself, when the diges- 

 tive apparatus is slightly disordered. 



550. The Lungs are capable, under peculiar circumstances, of absorbing fluid 

 from the atmosphere." Thus Dr. Madden* has shown that, if the vapour of hot 

 water be inhaled for some time together, the loss by exhalation is found to be 

 so much less than usual as to indicate that the cutaneous transpiration is partly 

 counterbalanced by pulmonary absorption ; the pulmonary exhalation being at 

 the same time entirely checked. It it probable that, if the quantity of fluid in 

 the blood had been previously diminished by excessive sweating, or by other 

 copious fluid secretions, the pulmonary absorption would have been much 

 greater. Still, in the cases formerly mentioned (465), in which a large in- 

 crease in weight could only be accounted for on the supposition of absorption 

 of water from the atmosphere, it seems probable that the cutaneous surface 

 was chiefly concerned ; for it can only be when the air introduced into the 

 lungs is saturated with watery vapour that the usual exhalation will be checked, 

 or that any absorption can take place. That absorption of volatile matter dif- 

 fused through the air is, however, continually taking place by the lungs, is 

 easily demonstrated. A familiar example is the effect of the inhalation of the 

 vapour of turpentine upon the urinary excretion. It can only be in this 

 manner that those gases act upon the system which have a noxious or poison- 

 ous effect, \vhen mingled in small quantities in the atmosphere. Of these, 

 sulphuretted hydrogen is one of the most powerful in its action ; for it has 

 been found that air impregnated with TI L-Qth part of it will kill a bird in a very 

 short time, and that a quantity but little more than double, namely ^th part, 

 will soon kill a dog. This gas is exhaled in large quantities from many forms 

 of decomposing animal and vegetable matter, and it has recently been shown 

 (by Professor Daniell) to be absorbed by the water of the estuaries of those 

 African rivers, whose mouths are regarded as among the most pestilential spots 

 upon the surface of the globe. Carburetted hydrogen is another gas whose 

 effects are similar, but a larger proportion is required to destroy life. 



551. Carbonic acid gas also appears to be absorbed by the lungs, when a 

 large proportion of it is contained in the atmosphere. The accumulation of 

 this gas in the blood, when the respired air is charged with it even to a mode- 

 rate amount, might be attributed to the impediments thus offered to its ordinary 

 exhalation ; but the following experiment appears to prove, that it may be 

 actually absorbed into the blood, and that it will thus exert a real poisonous 

 influence, and not merely produce an asphyxiating effect. It was found by 

 Rolando, that the air-tube of one lung of the land tortoise may be tied without 

 apparently doing any material injury to the animal, as the respiration performed 

 by the other is sufficient to maintain life for some time ; but, having contrived 

 to make a tortoise inhale carbonic acid by one lung whilst it breathed air by 

 the other, he found that the animal died in a few hours .t Cyanogen is another 

 gas which has an actively poisonous influence upon animals when absorbed 

 into the lungs ; its agency, also, is of a narcotic character. It is singular that 

 the effects of the respiration of pure oxygen should not be dissimilar. At 



* Prize Essay on Cutaneous Absorption, p. 55. 



f The fatal result of breathing the fumes of charcoal is, therefore, not simple asphyxia, 

 such as would result from breathing hydrogen or nitrogen. Other volatile products are 

 set free in the combustion of charcoal, besides carbonic acid. Mr. Cd|thupe (loc. cit.) 

 states these to be Carbonate, Muriate and Sulphate of Ammonia, Carbonic Oxide, Oxygen, 

 Nitrogen, Watery vapour, and Empyreumatic Oil: to these Sulphurous Acid may appear 

 to be properly added. 



