GENERAL PHYSIOLOGY OF THE EPITHELIUMS. 193 



brane;.in acute effusion of the peritoneum hypertrophy of 

 the epithelium of the serous membrane takes place, occasion- 

 ing, exactly as in the case of the mucous, the formation of 

 false membranes ; also, chronic effusion, when not produced 

 by mechanical causes, will be generally found to be the result 

 of deterioration of the epithelium. When medicines are 

 given to thicken the blood and excite the activity of certain 

 organs, if their effect is to dimmish the quantity of fluids in 

 the body, they generally fail of their purpose ; and yet, ac- 

 cording to physical laws, the effusion ought to be reabsorbed. 

 In order to bring about this result, the vitality of the epi- 

 thelium must be modified, by the introduction of irritating 

 substances (as, for instance, in vaginal effusions). On the 

 other hand, the application of physical laws to the functions 

 of the pleura would occasion the formation of a space 

 between its two folds and, consequently, of a constant liquid 

 effusion between them : this effusion takes place only in 

 pathological conditions of the serous membrane, that is, of the 

 epithelium which covers it; for in the normal state this 

 globular layer prevents any passage of fluid and any exhala- 

 tion from within outwards, exactly as the epithelium of the 

 bladder prevents any passage from without inwards, or 

 absorption. 



We may conclude, from all this, that the general property 

 of the epithelial globules is to choose their materials, to 

 borrow certain elements from the surrounding mediums, and 

 reject others. We shall see that the epithelium of the blad- 

 der repels fluids generally, without, however, being imper- 

 meable in the proper sense of the word ; it is impermeable 

 by election, for no doubt, the urine may be concentrated in 

 the bladder, but the water alone is absorbed without passage 

 of the dissolved matter. 1 In the intestinal canal we find that 

 the presence of certain substances, as a solution of sugar or 

 of albumen, produces no effect on the epithelial globule, but 

 that it enters immediately into action if these same sub- 

 stances be modified or accompanied by the gastric juice. 



The epitheliums, in short, are essentially living elements, 

 as is proved by the metamorphoses and functions found to 

 exist in the whole series of phenomena which we have gone 

 through. 



1 See J. C. Susini, " De I'lmperm^abilite de 1' Epithelium vesi- 

 cal." These de doctorat, Strasbourg, 18G7, No. 30. 



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