CAUSES WHICH PRODUCE VESICATION. 433 



from portions of the cutis on which were hairs which must 

 necessarily have perforated it, no foramina have appeared 

 in it. 



M. Bichat took very different ground : he asserted that the 

 pores of the separated cuticle were to be seen distinctly, in 

 large numbers, by looking through it towards the light ; he also 

 believed that the course of the exhalent vessels, through the 

 cuticle, might be seen in the same manner; and that they 

 passed obliquely. 



That the cuticle is pervious, is proved incontestably by the 

 functions of perspiration and sweating, as well as of absorption ; 

 but there are good reasons for believing that the perforations 

 of the cuticle have a peculiar structure ; and are not simple 

 foramina. Thus, when a vesicle is formed by the operation of 

 cantharides or any other process, if the cuticle is not lacerated, 

 it will confine the effused fluid for a considerable time, without 

 any appearance of its escape through these pores. 



This fact, which is strongly opposed to the hypothesis of 

 Meckel, is explained by Cruikshpnk upon the supposition that 

 the pores of the skin are lined by processes of the cuticle, and 

 that when the cuticle is separated from the cutis, these pro- 

 cesses go with it, and act like valves in confining the fluid. 



Bichat supposes the oblique vessels to produce the same 

 effect upon analogous principles ; and compares their situation 

 to that of the ureters, which pass obliquely between the coats of 

 the bladder. 



This peculiar quality of the cuticle, in admitting of perspira- 

 tion and sweat, and also absorption, while it prevents evapo- 

 ration from the parts which it encloses, is of immense impor- 

 tance. 



If a portion of skin be deprived of cuticle a short time before 

 death, by a blister for example, this portion will, in a few days, 

 become perfectly dry and hard, like horn ; while the other parts 

 of the skin of the subject, covered by the cuticle, retain their 

 moisture and flexibility. 



It may, therefore, be admitted, that the use of the cuticle is 

 to keep the -skin soft and flexible, by confining its moisture, as 

 37 



