22 REPORT 1841. 



proximated to, the microscope. (Numerous diagrams illustrating these various 

 stages were laid before the Meeting.) 



In the foetus, the defined and well-formed scales of the epidermis are not 

 unfrequently distinctly 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. On the surface of the vascular mucous membrane 

 minute cells are found tvifh a fiucleus internally, round tvhich the cells grow, 

 and this in short is the process of development of the epithelium. 



With respect to how the epithelium cells are connected together, a subject 

 which had not yet been discussed, Mr. Nasmyth stated, that on the surface 

 of the mucous membrane, the considerable spaces between them are occu- 

 pied by a gelatinous substance, interspersed with minute granular bodies. 

 This same substance also fills the minute linear intervals between the super- 

 ficial scales. (Diagrams were exhibited showing the arrangements in both 

 these cases.) The gelatinous medium is considerably elastic, as may be seen 

 under the microscope, on attempting to draw asunder the scales of the moist 

 epithelium. The scales towards the free surface distinctly overlap. The 

 granules of the gelatinous medium give to the epithelium, en masse, an 

 appearance of density as they sometimes cover the scales, but can be sepa- 

 rated from the latter, and indeed made to disappear entirely by compression. 

 In certain parts of the epithelium of the calf, distinct fibres pass over the 

 surface of the scales and connect them together, thus forming a very delicate 

 network, which is very evident on compression of the thick epithelium on 

 the anterior part of the alveolar arch of the upper jaw. 



On the skin and surface of the mucous membranes of man and animals 

 generally, the external layer of scales is continually being thrown off, in 

 consequence of pressure from those in process of development from beneath ; 

 after cuticular lamellae have been detached, their place is regularly occupied 

 again by newly formed scales. In some cases the external layer of cuticle 

 is removed, not scale by scale, but in a continuous form. The cuticle of the 

 frog is composed of minute scales, not overlapping, but in direct apposition, 

 forming one lamina of a beautiful, continuous, tessellated appearance. This 

 is thrown off at once from the entire bodies of frogs and efts. (Mr. Nas- 

 myth here displayed to the Meeting considerable portions of such a cuticle, 

 stating it to be his opinion, that this is the skin which is described by some 

 naturalists as being swallowed as soon as thrown off.) On a microscopic 

 examination of the skin of the frog, cells will be found internally, which 

 gradually change into the shape of scales, as they become more external, in 

 the same manner as has been described above. 



Mr. Nasmyth could not but conclude, from a consideration of the phae- 

 nomena j'ust described, that the cuticle and epithelium are organized tissues, 

 which are formed, as it appeared to him, from a fluid secretion on the surface 

 of the chorion; the various stages of development being, first, the formation of 

 nuclei and corpuscles; second, that of cells ; third, the growth of the latter 

 effected by vital imbibition ; fourth, their compression and gradual conversion 

 into minute lamellcE or scales. It appeared to him a rational conclusion, that 

 the component parts of the cuticle and epithelium have within themselves a 

 power of growth ; it remained for pathologists to determine what share the 

 derangement of this function has in the production of cutaneous diseases. 

 The ciliary motions and other vital phaenomena furnish new arguments for 

 the organic nature of the epithelium. 



Mr. Nasmyth concluded his paper by an especial notice of the epithelium 

 of the mouth. In the foetal subject, previous to the extrusion of the teeth, 

 this forms on the alveolar arch a dense, projecting layer, distinguishable by 



