126 PRACTICAL HISTOLOGY. [iV. 



precipitates the mucin of the saliva either in the form of fine threads 

 or in membranes, which are stained red by the magenta. 



3. Epidermis of Newt Superficial Layers of Stratified Epithe- 

 lium (L and H). Keep a newt or frog for a day or two in a small 

 quantity of water, and do not change the water. Very soon the super- 

 ficial layers of squames will be " cast " as thin membranes. Take 

 these, and harden them in absolute alcohol. Stain a thin piece in 

 hsematoxylin, and mount it in balsam. 



(a.) Try to get a layer sufficiently thin, so that the cells are only 

 one layer thick. Note the polygonal, large, nucleated cells united to 



each other by their edges by means 

 of a clear cement substance (fig. 85). 

 (b.) The nucleus is usually ex- 

 centric, and surrounded by slightly 

 granular material. In the nucleus 

 are usually two or three nucleoli, 

 and sometimes an intra-nuclear 

 plexus of fibrils is visible, especially 

 in the cells of the deeper layers. 

 Sometimes granules of the pigment 

 melanin are seen in the cells, especi- 

 ally from a dark-pigmented newt. 

 4. V.S. of Stratified Epithelium. 



FIG. 85. Superficial Layer of Squames This may be conveniently ex- 

 cast from the Epidermis of a Newt. , ,.J . - i A.* 



Alcohol and luematoxyiin, x 300. ami ned either in a vertical section 



of the skin of the palm of the 



hand, or a similar section of the mucous membrane covering the 

 hard palate of a cat or the conjunctiva on the cornea. The skin 

 must have been previously prepared by being hardened in absolute 

 alcohol or chromic acid and spirit mixture (p. 29), while the mucous 

 membrane may be hardened in the chromic acid and spirit or 

 Miiller's fluid. 



If the mucous membrane of the hard palate be taken, stain it 

 with picro-carmine and mount in Farrant's solution. Or the mucous 

 membrane may be stained in bulk in borax carmine, embedded and 

 cut in paraffin. In the latter case the sections are best mounted in 

 balsam. 



(a.) Examine it first with (L). Observe the epithelium arranged 

 in many layers, covering a connective-tissue basis the latter 

 stained red and projecting in the form of fine papillae into the 

 epithelial layer (fig. 86). Neglect the connective-tissue basis 

 meantime. 



(b.) (H) Select a thin part of the deeper layers of the epithelium 

 near the papillae, and note that the cells there arc somewhat small 

 and cylindrical, with their nuclei stained red. Study the change 



