316 ABSORPTION. 



These observations do much to reconcile the contradictory experiments of others, in some 

 of which a diminution in weight was observed, while in some an increase was noted. In 

 studying this subject, it must always be remembered that there is a constant loss of 

 weight by evaporation from the general surface and from the lungs; a fact which was 

 not taken into account by some of the earlier experimenters. 



It has been frequently remarked that the sensation of thirst is always least pressing 

 in a moist atmosphere, and that it may be appeased to a certain extent by baths. It is 

 true that, in a moist atmosphere, the cutaneous exhalations are diminished, and this 

 might account for the maintenance of the normal proportion of fluids in the body with a 

 less amount of drink than ordinary ; but we could hardly account for an actual allevia- 

 tion of thirst by immersion of the body in water, unless we assumed that a certain 

 quantity of water had been absorbed. A striking example of relief of thirst in this way 

 is given by Captain Kennedy, in the narrative of his sufferings after shipwreck, when lie 

 and his men were exposed for a long time without water, in an open boat. With regard 

 to his sufferings from thirst, he says: "I cannot conclude without making mention of 

 the great advantage I derived from soaking my clothes twice a day in salt-water, 

 and putting them on without wringing. . . . There is one very remarkable circum- 

 stance, and worthy of notice, which was, that we daily made the same quantity of urine 

 as if we had drunk moderately of any liquid, which must be owing to a body of water 

 absorbed through the pores of the skin. ... So very great advantage did we derive 

 from this practice, that the violent drought went off, the parched tongue was cured in a 

 few minutes after bathing and washing our clothes ; at the same time we found ourselves 

 as much refreshed as if we had received some actual nourishment." 



Absorption ly the Respiratory Surface. In studying the physiological anatomy of 

 the respiratory apparatus, we have seen how admirably the respiratory surface is calcu- 

 lated for the introduction of gaseous principles into the blood. The great rapidity with 

 which the oxygen of the inspired air penetrates through the delicate covering of the pul- 

 monary vessels has already been fully considered under the head of respiration. Under 

 natural conditions, the gases of the air are the only principles absorbed by the lungs ; but 

 examples of the absorption of other gaseous matters are exceedingly common, and this 

 process has been the subject of numerous experiments by physiologists. The fact of the 

 absorption of foreign substances by the lungs, also, has long been definitely settled ; but 

 this belongs to pathology or to therapeutics, rather than to physiology. 



It is now almost universally conceded that animal and vegetable emanations may be 

 taken into the blood by the lungs and produce certain well-marked pathological condi- 

 tions. It is supposed that many contagious diseases are propagated in this way, as well 

 as some fevers and other general diseases which are not contagious. With regard to cer- 

 tain poisonous gases and volatile principles, the effects of their absorption by the lungs 

 are even more striking. Carbonic oxide and arseniuretted hydrogen produce death al- 

 most instantly, even when inhaled in small quantity. The vapor of pure hydrocyanic acid 

 acts frequently with great promptness through the lungs. Turpentine, iodine, and many 

 medicinal substances may be introduced with great rapidity by inhalation of their va- 

 pors; and we well know the serious effects produced by the emanations from lead or mer- 

 cury in persons who work in these articles. Among the most striking proofs of the 

 absorption of vapors by the lungs are the effects of the inhalation of ether. This passes 

 into the blood and manifests its characteristic anaesthetic influence almost immediately. 

 Not only have vapors introduced in this way been recognized in the blood, but many of 

 the principles thus absorbed are excreted by the kidneys and may be recognized by their 

 characteristic reactions in the urine. 



As would naturally be expected, water and substances in solution, when injected 

 into the respiratory passages, are rapidly absorbed, and poisons administered in this way 

 manifest their peculiar effects with great promptness. Experimenters on this subject 



