IMJ5EUDING 81 



Portions of tissue so fresh as to be still warm are best 

 hardened in corrosive sublimate. They are left for from ten to 

 thirty minutes in a 5 per cent, solution prepared at 70° C, and 

 are then transferred directly into moderately dilute alcohol, 

 in which they remain for a day, and hardening is then 

 completed in absolute alcohol. 



Imbedding. — The hardened specimens are prepared for 

 section-cutting in many different ways, to enable them to be 

 fixed in the microtome. 



Imbedding in gum arabie. — One of the simplest methods 

 consists in fastening them with gum arable to cork or elder 

 pith, or to little bits of wood, when, after drying, sections 

 are cut from them, great care being taken to prevent the 

 hardened gum from injuring the knife. The process con- 

 sists in immersing the pieces to be cut in a concentrated 

 solution of gum arable of a syrupy consistence, after 

 imbedding in which they are deposited in concentrated 

 alcohol. This extracts the water from the gum, so rendering 

 the mass sufficiently firm to be cut. 



Imbedding in glycerine jelly. — The most useful method 

 is that of attaching the pieces to little bits of cork or wood 

 by means of a concentrated glycerine jelly prepared with 

 the aid of heat ; Frankel recommends boiling together one 

 part gelatine, two parts water, and four parts glycerine. 

 The portion of organ having been made to adhere by 

 means of this glycerine glue, nothing further is done until 

 the gelatine sets, when the piece is laid in alcohol and 

 becomes after some time so firmly adherent that the 

 cork can be clamped in the microtome and sections made. 

 It is necessary to bring the knife to the preparation 

 obliquely, and to keep everything constantly wet with 

 alcohol while cutting. Before staining, the sections must 

 always be brought into absolute alcohol. To enable gly- 

 cerine jelly to be kept in stock, a drop of corrosive subli- 



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