WITH THE MICROSCOPE. 143 



bare. The appearance of epithelium upon the surface of the vessel, 

 is caused by the loops of capillaries being shrunken and collapsed. 

 When distended with transparent injection, no such appearance is 

 observable, but here and there a few very small granular cells are 

 observed. Masses of germinal matter or nuclei, are connected with 

 the walls of these vessels, as well as those in other tissues. See p. 126. 



Organs of Innervatiou . 



243. Examination of the Brain. The brain may be subjected 

 to examination as soon as possible after death. In examining the 

 fresh brain, small portions may be removed on the end of a knife, 

 placed upon the glass slide, and moistened with a little serum, or 

 weak solution of sugar, but it must be admitted little can be learnt 

 by such a mode of examination, as the relation of the structures to 

 each other is completely destroyed. For examining the arrangement, 

 and distribution of the nerve fibres, portions of brain should be 

 hardened in the chromic acid solution, p. 57, when very thin sections 

 can be obtained with a sharp razor. Dilute solution of caustic soda is 

 also exceedingly useful for rendering the nerve tubes more distinct. 

 The minute anatomy of the brain may be studied in man and in the 

 higher animals. 



The examination of the dura mater and arachnoid is conducted 

 according to the general plan already laid down. Veiy small pieces 

 are removed, carefully torn up with needles, moistened with water, 

 and covered with thin glass. The gritty substances (brain sand) in 

 the pineal body, and those which are not unfrequently met with in 

 other parts of the brain, and the Has sail's corpuscles, or corpora 

 amylacea, may be separated from the brain substance by washing in 

 a glass of water, in which they will sink to the bottom ; the super- 

 natant fluid may then be poured off, and replaced by fresh water. 

 After this process has been repeated a few times, the bodies in ques- 

 tion will become quite clean. They may then be examined in water, 

 tested with appropriate reagents, and preserved in aqueous fluid, or 

 dried and mounted in Canada balsam. 



The vessels of the brain may be readily examined if the white 

 or grey cerebral matter be first removed by washing a thin section 

 with water. The addition of a little very dilute caustic soda renders 

 the outline more distinct. 



The investigation of the anatomy of the central organs of the 

 nervous system is perhaps the most difficult which the student can 

 undertake, and it is not easy to lay down principles for his guidance. 

 Very much yet remains to be discovered with reference to the 



