MICROSCOPICAL TECHNIQUE. 215 



is melted, the section turned and polished on the other side until 

 the required thinness is reached. Only compact tissue can be 

 prepared by this method. The spongy tissue, being delicate, must 

 be embedded before sectioning. This may be done according to 

 the method given by Wiel,* Koch's copal method, t or a mixture 

 of ten parts resin and one of ordinary wax may be used. J The 

 objects should be placed in a very fluid, but not too hot, solution 

 of the above, and after a short time lifted out with forceps, leaving 

 as much of the mixture as possible adhering to the object. When 

 cool, the mass may be cut into thin sections and ground in the 

 ordinary way, washed and cleaned in turpentine, and mounted in 

 balsam. If an opaque preparation be desired, the embedding 

 mass is removed by washing in chloroform and the sections dried 

 between sheets of filter-paper and mounted. 



A very convenient method is given by Ranvier.§ The frag- 

 ment of bone is placed in a syrupy solution of gum arable, and 

 when saturated it is exposed to the air until the gum thickens ; it 

 is then hardened in alcohol From this mass sections are made and 

 ground in the usual way, except that alcohol is used to wet the hone 

 instead of water. When ground sufficiently thin, the gum is dis- 

 solved in water and the section is ready to mount. According to the 

 method of mounting, either opaque or transparent preparations are 

 made. For the study of Haversian canals, lacunae, and canaliculi, 

 the former is better. To obtain an opaque preparation, a drop of 

 balsam is placed on the slide and heated over a spirit-lamp to 

 evaporate the oil. It is then cooled and tested by a needle. If 

 hard, the balsam is again softened and the dry section placed in 

 it ; at the same time a drop of balsam is placed on the cover- 

 glass, which is applied, and the whole transferred to a cold surface. 

 This should be done as quickly as possible, in order that the 

 balsam may solidify before penetrating the cavities. If, on the 

 other hand, we wish to study osseous lamellae as stained prepara- 

 tions, the section is first placed in a solvent of balsam, then trans- 

 ferred to a warm solution of balsam until the entire canalicular 

 system is filled, when it is mounted." 



* Zeit,f. I'Viss. Alikros., Bd. iv., p. 200, 1888. 



t Whitman's Embryological Methods^ p. 233. 



t Ehrenbaum, Zeit. f. IViss. Mikros., Bd. I., p. 14, 1884. § Traite^ p. 249. 



