226 THE MICROSCOPIST. 



Place a piece of human scalp, skin from palmar surface 

 of finger, and skin of dog (for muscles of hair-follicles) in 

 chromic and spirit fluid. In a month transfer to methy- 

 lated spirit. 



Remove the petrous portion of temporal bone, open the 

 tympanum, pull the stapes from the oval fenestra, and 

 place the cochlea in chromic and spirit fluid. Change in 

 eighteen hours, and at the end of seven days, if a brown 

 precipitate falls, change fluid every third day. On the 

 tenth or twelfth day transfer to chromic and nitric fluid. 

 Change frequently till the bone is soft. Then place it in 

 methylated spirit. The cochlea of the guinea pig pro- 

 jects into the tympanum, and is, therefore, convenient for 

 enabling the student to see how the cone is to be sliced 

 when sections are made. 



Too long exposure to chromic acid renders tissues fria- 

 ble, and prevents staining with carmine. 



Methylated spirit is ordinary alcohol containing 10 per 

 cent, of wood-naphtha, and is used in England as a sub- 

 stitute for alcohol, since it is free of duty for manufactur- 

 ing purposes. 



CHAPTER XIII. 



THE MICROSCOPE IN PATHOLOGY. 



PATHOLOGICAL histology treats of the minute anatomy 

 of the tissues and organs in disease, and is essential to a 

 knowledge of structural changes in the body. Since the 

 old method of judging solely by symptoms has given place 

 to the more rational observation of the actual changes 

 produced, the microscope has become an indispensable aid 

 to practical medicine. As anatomy would be coarse and 

 imperfect without histology, so pathological histology 



