668 APPENDIX. 



" The portion of skin being quite dry, it is to be removed from 

 the board, and, after cutting off the edge, several thin sections 

 may be made by the aid of a very sharp knife through the whole 

 thickness. In order to obtain a good specimen of the spiral por- 

 tion of the sweat-ducts, the skin of the heel should be selected, 

 and the section should be made parallel with the furrows, and in 

 a slightly slanting direction, instead of at a right angle with the 

 surface. 



" The sections may next be placed in a watch-glass, with a few 

 drops of clean water, and in the course of a short time it will be 

 found that they have again attained the original thickness of the 

 skin, in consequence of the absorption of water. They may now 

 be submitted to examination, and after selecting a satisfactory 

 specimen, it may be mounted in weak spirit and water, Goadby's 

 solution, or other preservative fluid ; or, the specimen may be 

 washed in water, placed upon a slide, and allowed to dry slowly 

 by spontaneous evaporation (when it will be found to have ad- 

 hered tightly to the glass), and mounted in Canada balsam, with 

 the usual precautions." 



Any opacity of the preparation may be removed by a weak 

 solution of potash or caustic soda. Soaking in ether will dis- 

 sipate the fat. The sweat-glands are made more distinct by 

 soaking the tissue in a mixture of one part of nitric acid and two 

 of water. 



Large flakes of cuticle may be obtained for examination by ex- 

 posing a small piece of skin to a moist atmosphere for several 

 days. The superficial cells of the cuticle are brought into view 

 by scraping the surface of the skin with a knife. These cells are 

 flattened and adherent, and present a scaly appearance. The 

 deeper-seated epidermic cells are more or less round, and appear 

 to rest upon a layer of very minute granules mixed with coloring 

 matter. The deep cells are soluble in acetic acid ; the superficial 

 are not. On the under surface of the cuticle are found a number 

 of depressions,, which receive the tactile papillae of the cutisvera. 



The papillae may be studied either upon a vertical section 

 made in the manner above described, or upon a section of the 

 cutis itself, the cuticle having been first removed. From tneir 

 large size, the papillae of the skin of the dog's foot are well 

 adapted for examination. The papillary vessels are best seen in 

 an injected specimen, while the nerves and " axis-corpuscles" are 

 sometimes brought into view by the addition of acetic acid or a 

 weak solution of caustic soda. 



The pigmentary cells are best seen in the skin of the negro, in 

 that of some of the lower animals, and also in freckled surfaces. 



Cutaneous Eruptions, Growths, Ulcers, $c. Corns, callosities, 

 and condylomatous warts consist of condensed epidermic scales. 

 In Yeruca achrocordon, the scales are collected around a central 

 canal supplied with bloodvessels. Small cutaneous tumors are 

 sometimes formed by the thickening of the subjacent areolar 



