Caldwell's automatic microtome. 653 



slide while moist, and place it in the dry shelf of the water 

 bath, which should be at a temperature slightly above the 

 melting point of the embedding material used. It should be 

 left here until the creosote has evaporated and the embedding 

 material melted. Now allow the slide to cool, and then wash 

 it with turpentine until all the embedding material is dissolved. 

 Canada balsam in chloroform or turpentine and the cover slip 

 may now be applied in the usual manner. For convenience of 

 mounting, it is extremely important that the ribbon of sections 

 should be quite straight, and in order to ensure this it is neces- 

 sary that the sides of the embedding material from which the 

 sections are cut should be quite parallel. The straight ribbon, 

 when obtained, should be removed to some clean surface and 

 there cut into lengths appropriate to the size of the cover slips 

 used. It will be found convenient to use cover slips at least 

 two inches long : indeed a useful length for slides and cover 

 slips is six inches for the former and four inches for the latter. 

 A Method of Embedding the Specimen to be Cut. — 

 After the specimen has been stained it should be left in 90 per 

 cent, alcohol for a few minutes, and thence transferred to 

 absolute alcohol, there to remain until all the water is extracted. 

 The length of time necessary for this varies greatly with the 

 size of the specimen. A three-day chick, for instance, will 

 require about an hour, larger specimens a day or more, in 

 which case the absolute alcohol should be changed occasionally. 

 Some tissues may be transferred directly from the absolute 

 alcohol to turpentine, and thence in about two hours to the 

 melted embedding material. For delicate tissues, however, the 

 following process, though longer and more troublesome, is 

 greatly preferable. With a pipette, introduce some chloroform 

 to which two or three drops of ether have been added, under 

 the alcohol in which the object is lying. The object will then 

 float for some time at the junction of the alcohol and chloro- 

 form, and will finally sink into the chloroform when saturated 

 with it. If, as often happens in the case of embryonic tissues, 

 the object is lighter than the chloroform, it is not easy to tell 

 when the saturation is complete, but generally on shaking the 



