THE MICROSCOPE IN ANIMAL HISTOLOGY. 217 



root has a ganglionic enlargement, and contains only sen- 

 sory fibres ; the latter has no ganglion, and contains only 

 motor fibres. 



The cerebral nerves are those given off from the base 

 of the brain. Some of these minister to special sensation, 

 as the olfactory, optic, auditory, part of the glosso-pha- 

 ryngeal, and the lingual branch of the trifacial nerves. 

 Some are nerves of motion, as the motor oculi, patheti- 

 cus, part of the third branch of the fifth pair, the abdu- 

 cens, the facial and the hypoglossal nerves. Others are 

 nerves of common sensation, as the fifth, and part of the 

 glosso-pharyngeal nerves. Others, again, are mixed, as 

 the pneumogastric and spinal accessory nerves. 



The minute structure of the central organs of the ner- 

 vous system is excessively complicate and full of details. 

 Hardening with chromic acid and bichromate of potash 

 is generally advisable before examination. This should 

 be done with small pieces in a large quantity of the fluid. 

 One-eighth to one-half grain of bichromate, or 0.033 to 

 0.1 grain of chromic acid, to the ounce of water should 

 be used, the strength gradually increased from day to 

 day. After such maceration for several days, a drop of a 

 28 per cent, solution of caustic potash may be added to 

 one ounce of water, and the specimen soaked in it for an 

 hour, to macerate the connective tissue. After again soak- 

 ing in graduated solutions of the bichromate, up to two 

 grains to the ounce, the tissue may be carefully picked 

 apart under the dissecting microscope. In such manner 

 Deiters discovered the two kinds of processes in the multi- 

 polar ganglion-cells. Gerlach placed thin sections for two 

 or three days in 0.01 to 0.02 per cent, solutions of bichro- 

 mate of ammonia, and picked them apart after staining 

 with carmine. 



Lockhart Clarke placed parts of the spinal cord in equal 

 parts of alcohol and water for a day, then for several days 

 in pure alcohol, till thin sections could be made. These 



