296 ABSORPTION AND SANGUIFICATION. 



5. Absorption from the External and Pulmonary Surface. 



522. Although the Mucous Membrane of the Alimentary Canal is 

 the special channel for the introduction of nutritive or other substances 

 into the system, it is by no means the only one. The Skin covering 

 the body, and the Mucous Membrane prolonged into the Lungs, are 

 also capable of absorbing liquids and vapours, and of introducing them 

 into the Circulation ; although they serve this purpose less in Man 

 and the higher animals, than in some of the lower. Their utility in 

 this respect is best shown, when, from peculiar circumstances, the 

 function of the digestive cavity cannot be properly performed ; and 

 when, therefore, the system has been more than usually drained of its 

 fluids, and stands in need of a fresh supply. Thus shipwrecked sailors, 

 and others, who are suffering from thirst, owing to the want of fresh 

 water, find it greatly alleviated, or altogether relieved, by dipping 

 their clothes into the sea, and putting them on whilst still wet, or by 

 frequently immersing their own bodies. In a case of dysphagia, in 

 which neither solid nor fluid nutriment could be introduced into the 

 stomach, the patient was kept alive for a considerable time, and his 

 sufferings greatly alleviated, by the administration of nutritive clysters, 

 and by the immersion of his body in a bath of tepid milk and water, 

 night and morning. Under this system, the weight of the body, which 

 had previously been rapidly diminishing, remained stationary, although 

 the amount of the excretions was increased : and the use of the bath 

 had a special influence in assuaging the thirst, which was previously 

 distressing. It appeared that the water of the urinary excretion, 

 amounting to from 24 oz. to 36 oz. per day, must have been entirely 

 supplied from this latter source. Again, a man who had lost nearly 

 31bs. by perspiration, during an hour and a quarter's labour in a very 

 hot atmosphere, regained 8 oz. by immersion in a warm bath at 95 for 

 half an hour. In these cases it appears probable, from the experiments 

 already noticed ( 502), that the Lymphatics, rather than the blood- 

 vessels, are the chief agents in the absorbing process ; not, however, 

 from any powers peculiar to them, but merely on account of the thin- 

 ness of their walls, and their very copious distribution in the skin. 



523. Absorption may also take place from an atmosphere saturated 

 with watery vapour. Of this we have a very curious proof in the 

 Frog ; whose urinary bladder (which serves as a sort of reservoir for 

 water) has been observed to be refilled, after having been emptied, by 

 placing the animal in an atmosphere loaded with watery vapour. 

 Numerous instances are on record which prove that such absorption 

 may take place in Man, to a very considerable extent; though the 

 proportion introduced through the Skin, and through the Lungs, can- 

 not be exactly ascertained. The ready introduction of volatile matter 

 into the system, through the latter channel, is a matter of familial- 

 experience ; thus tf we breathe an atmosphere through which the 

 vapour of turpentine is diffused, it soon produces the characteristic 

 odour of violets in the urinary secretion. And it is probably in this 

 manner, that a large number of those putrescent miasmata and other 

 zymotic poisons are introduced, which are such fertile causes of disease. 



