Proceedings of the British Association. 131 



not unfrequently seen externally ; the rete malpighii consists of newly- 

 formed cells; and between the two may be observed other cells, in a 

 state of progressive development. In the epithelium generally, a 

 nucleus is first foi*med, and then a cell is formed around it. These cells 

 are connected by a gelatinous substance, interspersed with minute gran- 

 ular bodies, which displays considerable elasticity, and which sometimes 

 presents a fibrous appearance. The granules can be caused to dis- 

 appear by compression. In certain parts of the epithelium of the calf, 

 distinct fibres are observed to pass over the surface of the scales, and to 

 connect them together, thus forming a very delicate net-work. On the 

 surface of the body and of the mucous membranes of a man and animals 

 generally, the superficial scales are thrown off by pressure from the 

 cells beneath j but in some cases, as with frogs and efts, the epithelium 

 scales are removed in a continuous layer ; and Mr. Nasmyth is disposed 

 to believe that it is the covering which, according to naturalists, is 

 swallowed by the animal after having been shed. The cuticle and epi- 

 thelium then are evidently organized bodies. It would appear that 

 they are formed from a fluid secretion, and that their various stages of 

 development are as follows : 1st, the formation of nuclei and their 

 corpuscles ; — 2nd, that of cells ; — 3rd, the growth of the latter effected 

 by vital imbibition ; — 4th, their compression and gradual conversion 

 into minute lamellae, or scales. The cells seem to have within them- 

 selves a power of growth, and it remains for pathologists to determine 

 what share the derangement of this function has in the production of 

 cutaneous diseases. Under certain modifications, the epithelium cer- 

 tainly presents vital phenomena, among which may be mentioned the 

 ciliary motions. Mr. Nasmyth concluded his paper by an especial des- 

 cription of the portion of the epithelium lining the cavity of the mouth. 

 In the foetal subject, previous to the extrusion of the teeth, it forms on 

 the alveolar arch a dense projecting layer, distinguishable from the sur- 

 rounding membrane by its whiteness, and by superficial and waving 

 ridges and sulci. The younger the subject, the greater is its thickness. 

 It is made up of a mass of scales, lying one above the other, and thus 

 presents no resemblance to cartilage though it has been generally clas- 

 sed as such. In the interior of its structure, where it corresponds to 

 the molar teeth, small vesicles may be frequently observed, varying in 

 size from one-fourth to one-eighth of a line in diameter. On microscopic 

 examination, the particles of these are found to consist of attenuated 

 scales, and their cavity to contain a fluid abounding in minute granules 

 and cells. They are probably the " glands" described by Serres as in- 

 tended for the secretion of the tartar. Larger vesicles are also found 

 implanted in the vascular mucous membrane, composed of a very deli- 

 cate tissue, and containing a transparent fluid, which coagulates on the 

 application of heat or acid. In this fluid float numerous globules and 

 scales, similar to those of the epithelium generally. The internal, or 

 attached surface of the alveolar epithelium presents numerous fringed 



