420 ABSORPTION 



ABSORPTION FROM THE SKIN, THE LUNGS, ETC. 



The dry corneous stratified epithelium covering the human body pos- 

 sesses great resistance to the absorption of most substances. The sebaceous 

 secretion keeps the surface slightly oily. Watery solutions do not readily 

 wet the surface and therefore do not penetrate. There is some absorption 

 of water on prolonged contact with the skin, but the amount is insignificant. 

 Medicated baths, especially hot baths, may be accompanied by some slight 

 absorption of the substances dissolved in the waters, though it must be con- 

 fessed that the primary good effects of such treatment come from other 

 sources. 



On the other hand, oily substances come in more intimate contact with 

 the skin and penetrate deeper and more readily. Therefore, lotions con- 

 taining medicines are occasionally applied to the skin, and slow but gradual 

 absorption occurs. The volatile oils penetrate the skin readily. 



The epithelial lining of the lungs seems peculiarly adapted to the quick 

 absorption of gases and volatile substances. This is illustrated by the 

 rapidity of adjustment of the body to variations in pressure in the inert 

 nitrogen of the air in caisson work and in aviation. The volatile anes- 

 thetics, ether and chloroform, penetrate the pulmonary epithelium with 

 greatest facility. The same is true for other volatile substances. There is 

 increasing evidence that most substances soluble in water penetrate the 

 pulmonary epithelium with facility, and that this may in the future 

 become a more used channel for administering medicines. 



Solutions injected into or otherwise brought into contact with the sub- 

 dermal connective tissue, the surface of the body of a muscle, or intra- 

 muscularly, or within the peritoneal or thoracic cavities, very quickly pass 

 into the general circulation. They are practically injected into the lymph- 

 atic intercellular spaces in these instances and, of course, are very readily 

 carried through the lymphatic vessels, figures 280 and 282, to the thoracic 

 duct and into the blood. Readily diffusible substances, however, pass 

 directly through the blood capillary walls and do not necessarily follow the 

 longer lymph channel route. Comparing the rapidity of absorption in the 

 cases mentioned, that from the muscle is most rapid, a fact of medical im- 

 portance in the use of the hypodermic needle for the giving of medicines 

 in emergency. 



