54 ORGANS OF DIGESTION. 



the opposed surfaces of the deep wrinkles about their thighs and 

 in their perineum; a tendency obviated by the practice of nurses 

 of covering these surfaces with powdered starch. It is also 

 manifested frequently in the dressing of wounds with sticking 

 plaster, where an incautious approximation of the contiguous 

 surfaces of the skin, not only is followed by excoriation, but even 

 by ulceration; a fact, the importance of which was formerly set 

 in proper relief by Dr. Physiak in his surgical lectures, and of 

 which I have seen an example in a case of extirpated female 

 mamma. The state of this question is, in fine, such that I think 

 we may safely admit the existence of a very thin epidermis on 

 the alimentary canal, but so pulpy that it cannot be distin- 

 guished except by the process alluded to in Section third of this 

 Chapter. 



The mucous membranes vary in colour from a very light pink 

 to a deep red, which is owing to the blood that circulates in 

 them. In cases of suffocation, they become almost brown from 

 the congestion of blood in them, while in fainting they turn white 

 from the desertion of the latter. The vessels after having pe- 

 netrated the thickness of the membrane, ramify with extreme 

 minuteness on its surface. The veins in an injection invariably 

 predominate over the arteries by their greater size and disten- 

 sibility. In consequence of their superficial situation, the ves- 

 sles being unsupported on one side, are exposed to rupture from 

 slight concussions; in this way hemorrhage is produced in the 

 lungs from coughing, and bleeding at the nose from blows upon 

 the head. 



Exhalent orifices exist in great numbers in the mucous mem- 

 branes: this is especially the case in the lungs, where the pul- 

 monary perspiration, as it is called, is very obvious to common 

 observation. Elsewhere, this discharge is so much blended with 

 the mucus of the part, that it is difficult to appreciate its quantity. 

 From the superficial situation of the blood vessels, it is clear 

 that the exhalent orifices or pores, have but a short course to 

 run. This is considered by Bichat as a satisfactory reason for 

 the tendency of the blood to escape through them, or to ooze 

 out where there is no rupture. 



Absorbents exist also in great numbers, as proved by the ab- 

 sorption of chyle, of watery drinks from the intestinal canal, 

 and by the inhalation of the vapour of spirits of turpentine into 



