Ill 



THE NOSE. 



(A.) OLFACTORY EPITHELIUM OF THE FROG OR NEWT. 



PREPARATION, (a) Dilute Alcohol. Cut off the head of a newt or frog, and slit up the 

 nostrils with scissors ; place it in a small quantity of dilute alcohol for twenty-four hours. 

 Stain the whole head With picrocarmine, and tease a little of the stained epithelium from the 

 olfactory region in a drop of glycerine. This is the best method. 



(V) Maceration for two days, in a quarter per cent, solution of potassic bichromate, yields 

 fair results. 



(c] Maceration of the entire head in a half per cent, solution of osmic acid for five hours, 

 followed by steeping in water, also ' fixes ' the cells. 



EXAMINATION (H). Observe the ordinary columnar epithelial cells, devoid of cilia, but 

 amongst these observe the narrow, delicate, spindle-shaped cells, each with a spherical nucleus. 

 These are the true olfactory cells. To their free end a bunch of fine bristles is attached. Their 

 lower or fixed end consists of a very fine filament with varicosities on it. It is directly 

 continuous with the terminations of the fibres of the olfactory nerve. The olfactory cells are 

 richly scattered amongst the above-described cylindrical epithelium. (Indicate these cells in 

 PI. XXVII., Fig. 2.) 



(B.) Similar preparations may be made of the olfactory cells from the olfactory region of 

 the nose of a mammal. In this case the olfactory cells are devoid of bristles on their free 

 ends. 



(C.) OLFACTORY EPITHELIUM OF A MAMMAL. 



PREPARATION. Divide, by means of a saw, the head of a freshly-killed rabbit, dog, guinea- 

 pig, or sheep in a longitudinal direction, and parallel to the nasal septum. Cut out the nasal 

 septum so as to expose the olfactory region, easily recognised by its brown colour. Harden 

 this in Miiller's fluid for two days, and then transfer it to the chromic acid and spirit 

 mixture for a week. Complete the hardening in weak, and then in strong, spirit. Make 

 vertical sections, and stain them with logwood, and mount them in dammar or Farrant's 

 solution ; or a double-staining of logwood and picrocarmine may be employed. 



EXAMINATION (L). Observe the mucous membrane, covered by columnar epithelium. 

 The upper row of nuclei seen belongs to the supporting or columnar cells ; the deeper row 

 belongs to the true olfactory cells. In the deeper layers of the epithelium, and also in the 

 glands, are pigment-granules. Sections of gland-ducts and alveoli, filled with granular-looking 

 cells Bowman's glands are readily seen. (H). Examine the individual parts. (Indicate the 

 olfactory epithelium and Bowman's glands in PI. XXVIL, Fig. i.) 



