618 SPECIAL PHYSIOLOGY. 



posing and insulating such a vein in an animal, and placing poison 

 upon it, when death has followed. Absorption is favored by moderate 

 temperatures, but is retarded by temperatures much higher, or much 

 lower, than that of the blood. 



The rate of absorption of certain substances is very rapid ; ferro- 

 cyanide of potassium introduced into the stomach, has been found in 

 the urinary excretion after the short space of 60 seconds ; but when 

 the stomach is more or less full the absorption is retarded accordingly. 

 (Erichsen.) The rapid passage of saline substances into the saliva has 

 been shown by Bernard. Alcohol is absorbed so quickly, that its 

 eifects on the brain, when injected into the stomach of dogs, are almost 

 immediate, death occurring in about two minutes, the stomach being 

 then found to be empty, and the blood to contain large quantities of 

 alcohol. (Percy.) 



Substances once introduced into the veins, by absorption, are car- 

 ried with the blood to the heart, and thence along the arteries to every 

 part of the body. The condition of the circulation materially affects 

 the rapidity of absorption. If the vessels be full of blood, or even if 

 they be artificially injected with water, it is found that water intro- 

 duced into the pleura is absorbed more slowly (Magendie) ; if the ves- 

 sels be emptied by previous venesection, absorption takes place more 

 rapidly. Absorption is also more active, when the water of the body 

 has been diminished by abstinence from fluids, or by unusual excretion. 

 It is often suggested, that persons about to expose themselves to con- 

 tagion or malaria, should previously take food, so as to diminish the 

 chances of absorption, which is believed to be more likely to occur when 

 the bloodvessels are in a comparatively empty state, or when the sys- 

 tem is imperfectly nourished. The supposed immunity may be due to 

 the less exhausted condition of the nervous system, or to some other 

 unrecognized power of resisting diseased influences. 



The process of absorption by the bloodvessels is so dependent upon 

 the movement of the blood, that if a ligature be placed on those ves- 

 sels in the limb of an animal, or entirely around the limb, either, in 

 the former case, absorption takes place slowly through the lymphatic 

 vessels only, or, in the latter case, it does not occur at all. Thus, if a 

 poison be inserted under the skin of an animal's foot and a tight band- 

 age be applied round the limb, no symptoms of general poisoning ensue ; 

 but if the bandage be then removed, and the circulation through the 

 limb be restored by gentle friction, poisoning, or even death will occur. 

 Hence, the immediate ligature of a limb above a wound inflicted by a 

 poisonous serpent, will arrest the further entrance of the venom into 

 the circulation. The application of cupping-glasses to a poisoned wound, 

 operates, not merely by drawing out portions of the poison, owing to 

 the removal of atmospheric pressure from the part, but, also, by stagna- 

 ting the circulation in the injured and adjacent parts ; sucking a 

 poisoned wound acts in a similar manner. In a certain degree, the 

 destruction of the part by caustic, or the actual cautery, also operates 

 thus, but also by the simultaneous destruction of the poison itself. The 

 prompt removal of the poisoned tissues also arrests further absorption. 



The process of absorption is influenced by the nervous system, for, 



