170 IMBEDDING METHODS. 



could otherwise only be obtained by the employment of 

 chemical processes such as prolonged treatment with chromic 

 acid and the like. 



These ends are usually attained in one of two ways. Either 

 the object to be imbedded is saturated by soaking with some 

 material that is liquid while warm and solid when cold, 

 which is the principle of the processes here called Fusion 

 Imbedding Methods; or the object is saturated with some 

 substance which whilst in solution is sufficiently fluid to 

 penetrate the object to be imbedded, whilst at the same time, 

 after the evaporation or removal by other means of its solvent, 

 it acquires and imparts to the imbedded object sufficient firm- 

 ness for the purpose of cutting. The collodion process suffi- 

 ciently exemplifies this principle. If a piece of soft tissue be 

 dehydrated, and soaked first in ether and then in collodion, 

 and if the ether contained in the collodion be allowed slowly 

 to evaporate, the tissue and surrounding mass of collodion will 

 acquire a consistency such as to admit of thin sections being 

 cut from them. The methods founded on this principle are 

 here called Evaporation Imbedding Methods. 



The now antiquated egg-emulsion process, in which a mass 

 that is liquid whilst cold is coagulated by heat, or other 

 agency, belongs to a third class, which may be described as 

 Coagulation Methods. 



In any of these cases the material used for imbedding is 

 technically termed an " imbedding mass" Einbettungsmasse 

 masse d f inclusion. Imbedding methods are spoken of by 

 French writers as methodes d'inclusion, or methodes d'enrob- 

 age. 



273. Imbedding Manipulations. Before proceeding to de- 

 scribe in detail the more important imbedding methods, it is 

 necessary to give an account of the manipulations of the pro- 

 cess of imbedding in general. 



Imbedding in a melted mass such as paraffin is performed 

 in one of the following ways. A little tray or box or thimble 

 is made out of paper, some melted mass is poured into it ; at 

 the moment when the mass has cooled so far as to have a 

 consistency that will not allow the object to sink to the 

 bottom, the object is placed on its surface, and more melted 

 mass poured on until the object is enclosed. Or the paper 



