ABSORPTION. 87 



the organic tissues change incessantly during their progress, 

 borrowing or lending elements to each one of the molecules 

 through which they pass. And farther, the different tissues 

 absorb more or less of the same substance by virtue of pro- 

 perties which are unknown. In this way a poison which 

 remains inert on the mucous membrane of the stomach is 

 rapidly absorbed by the lungs. 



The mucous membranes absorb more rapidly than the 

 skin, and this tissue is more or less permeable according to 

 its thickness, its density, as the epidermis which covers it is 

 thick or thin. Absorption is therefore very rapid in inocula- 

 tion that is, when the substance to be absorbed is intro- 

 duced into the substance of the tissues. Wherever the point 

 of absorption may be, it takes place by the lymphatic vessels, 

 and especially by the veins. The veins absorb a greater 

 number of substances than the lymphatics, and carry them 

 more quickly into the circulation; they charge themselves 

 especially with the materials which are to be rejected from 

 the economy, while the lymphatics absorb from preference 

 those that can still be assimilated. The veins and the 

 chyliferous vessels, which are a variety of the lymphatics, 

 draw from the mucous membrane of the intestine the useful 

 products of digestion ; but the lymphatics take possession of 

 fats, while the veins prefer fluids, albumen, sugar, and salts. 



It is well known with what rapidity certain substances 

 taken into the alimentary canal, or into the lungs, pass into 

 the other organs, and exhale, or are eliminated. Thus the 

 presence of the ferro-cyanide of potassium has been recog- 

 nized in the urine within one minute after its ingestion into 

 the stomach. Indigo, gallic acid, and other colouring 

 matters, or those possessing a characteristic odour, pass in 

 the course of fifteen or twenty minutes through all the wind- 

 ings of the circulation. 



As has already been stated, absorption takes place much 

 more rapidly by the skin when it has been deprived of its 

 epidermis. Five or six minutes are generally a sufficient time 

 for the alkaloids of opium or belladonna to manifest their 

 action on the nervous system, and in some cases this action 

 is produced in a few seconds. Other substances, especially 



