1892.] Microscopy. 533 



by hones of finer grain, and finally polished on a piece of smooth 

 leather or buckskin covered with powdered chalk. 



Another method is to grind the bone on a glass plate with emery of 

 different degrees of fineness. This may be accomplished by pressing 

 the section down with the fingers, or it may be fastened to a cork by 

 means of sealing-wax or thick balsam. It is then polished on one side 

 until smooth ; then the wax or balsam 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 tis- 

 sue, being very delicate, must be imbedded before sectioning. This 

 may be done according to the method given by Wiel, 1 Koch's copal 

 method 2 or a mixture of ten parts resin and one of ordinary wax may 

 be used. 3 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 for- 

 ceps, 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 cleared in turpentine and mounted in bal- 

 sam. If an opaque preparation be desired the imbedding mass is 

 removed by washing in chloroform and the section dried between sheets 

 of filter paper and mounted. 



A very convenient method is given by Ranvier. 4 The fragment of 

 bone is placed in a syrupy solution of gum arabic, and when satur- 

 ated it is exposed to the air until the gum thickens ; it is then hard- 

 ened in alcohol. From this mass sections are made and ground in the 

 usual way, except alcohol is used to wet the hone instead of water. 

 When ground sufficiently thin the gum is dissolved 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 



x Zeit. f. wiss. Mikros., Bd. iv, p. 200, 1888- Abstract Am. Nat., xxiii, p. ol'O, 



2 Whitman's Embryological Methods, p. 233. 



