616 SPECIAL PHYSIOLOGY. 



moval ; thus, the surface of the true skin, exposed in blisters, absorbs 

 with great facility and rapidity; the unprotected and highly vascular 

 surface of the cutis is no longer able to resist the entrance of the most 

 deleterious substances; and even the cantharidin, or active principle 

 of the Spanish fly, used for producing the blister, is itself, sometimes, 

 in this way absorbed. It has been stated that the lymphatics of the 

 skin, which are very numerous and large, and have very thin walls, 

 absorb adventitious substances, perhaps, more readily than the blood- 

 vessels ; the reverse, however, is the case with the lacteals. 



The serous and synovial membranes also absorb, sometimes even 

 very rapidly. Poisons injected into the pleural and peritoneal cavities, 

 in living animals, are found to be most quickly taken up. Moreover, 

 the serous exudations which occur in inflammation of these membranes, 

 into the pericardial, pleural, and peritoneal cavities, are more or less 

 rapidly removed by the curative process of resorption; the fluids poured 

 out into the joints, in cases of rheumatic or other inflammation, and 

 even blood extravasated into those cavities, are also, though more 

 slowly, absorbed. The rapid absorption of the cerebro-spinal fluid (p. 

 236) affords another instance of the facility of absorption from an in- 

 ternal cavity ; so likewise does the absorption of blood and other effused 

 matters, and even that of the broken and non-dissolved cataractous 

 lens from the interior of the eyeball. 



Absorption from the areolar connective tissue is proved by the tak- 

 ing up, from its interspaces, of dropsical fluids, or effused blood ; also 

 by the poisonous effects of agents introduced experimentally into the 

 areolar tissue in animals; and lastly, by the effects of the hypodermic 

 or subcutaneous injection of solutions of morphia, or other medicinal 

 agents, into the living human body, for the relief of neuralgic pain, 

 and of the suffering after severe operations, or for the purpose of in- 

 ducing sleep, or of relieving obstinate cough or other irritation. 



Lastly, absorption from the artificial surfaces of ulcers and wounds, 

 is shown by the taking up of medicinal or poisonous substances, such 

 as mercury, arsenic, morphia, atropine, coniurn, and other substances, 

 applied to granulating sores. 



The vessels concerned in general absorption in the vascular tissues, 

 are the bloodvessels and lymphatics ; but in the non-vascular tissues, 

 as well as in non-vascular animals, absorption must take place by direct 

 permeation into the cells or other tissue elements. 



Absorption by the veins, or venous absorption, is proved by cutting 

 across the limb of an animal, excepting its chief artery and vein, and 

 then applying strychnine below the place of section, when the poison will 

 still act, being conveyed in the blood of the undivided vein. Poisoning 

 still takes place, if the artery and vein be also divided, and then rejoined 

 by pieces of quill, so that the poison cannot be imbibed and conveyed 

 by the coats of the vessels, but can only pass along the venous blood 

 current. To show that the poisoning does not take place through the 

 nerves, all parts of a limb may be divided, excepting the chief nerve, 

 when poison, applied to it, does not affect the animal. Absorption by 

 the veins generally, has also been proved by blistering the skin, apply- 

 ing a solution of ferro-cyanide of potassium, and, after a time, exam- 



