HISTOLOGICAL DEMONSTRATIONS. 137 



and preserve in Farrants' solution. The olfactory cells are 

 long and I slender, with a large nucleus about the centre. 

 The ordinary epithelial cells are much broader. In the 

 newt and frog the former have delicate hairs on their peri- 

 pheral extremities, but these can rarely be seen. 



SPINAL CORD AND MEDULLA OBLONGATA. 



244. Methods. a. The spinal cord and medulla 

 oblongata may be hardened by immersion in rectified spirit 

 followed by a ^ per cent solution of chromic acid (Lock- 

 hart Clarke] as directed in 14. Sections are made in a 

 microtome with the cord imbedded in carrot or paraffin. 

 The sections may be stained with carmine or logwood. 

 The former gives good results if the staining be very 

 slowly done. The dilution of Beale's carmine fluid with all 

 the ammonia retained ( 318, a) produces excellent results. 

 Twenty-four hours or more may be required. Carmine 

 may, however, completely fail if the tissue have been 

 over-hardened by chromic acid. In that case the carmine 

 staining may be readily effected after the previous action of 

 palladium chloride, as described in 3 1 9, or the sections 

 may be stained with logwood. 



b. The sections, whether stained or unstained, are 

 usually mounted in dammar. 



c. A method for isolating the nerve cells of the cord 

 has been already described in 156. 



245. Structure of the Cord. a. T. S. spinal cord of 

 cat carminised. Mount in dammar ( 152). 



(L.) The anterior and posterior median fissures. The 

 gray matter brightly stained with carmine. The nerve roots 

 may perhaps be seen ; the anterior forming two or three 

 bundles, the posterior only a single bundle. The anterior, 

 lateral, and posterior white columns in each half of the cord. 

 The gray (posterior) and the white (anterior) commissures 

 uniting the two halves of the cord. The central canal in 

 the gray commissure. Leave the canal exactly in the centre 

 of the field, and change the lens. 



(H.) The central canal lined by a single layer of ciliated 



