ON STAINING FLUIDS, AND STAINING. 109 



size of a pea, in sufficient strong methylated spirit 

 to dissolve them thoroughly. 



Soften some isinglass in water, remove all the 

 water and dissolve it in two ounces of absolute 

 alcohol. 



To this add two small pieces of gum ammoniacum 

 rubbing them up in a mortar until they are dissolved. 



Mix the two solutions, and keep the cement in a 

 wide mouthed stoppered bottle. 



When using it place the bottle in hot water until 

 the cement is liquefied. 



Embedding and Freezing. 



The great desideratum in embedding specimens, 

 for the purpose of making sections of them, is, that 

 they shall be firmly and equably supported in all 

 directions and that no distortion, displacement or 

 injury to the tissues, organs or organisms embedded 

 shall result. It is therefore most important that 

 the student should acquire the knowledge and 

 experience necessary to enable him to decide which 

 process will afford and ensure the delicacy combined 

 with solidity required in special cases. 



The methods of embedding are twofold, " simple " 

 and " interstitial," the former consisting in enclosing 

 the specimen to be sectionised in a soft substance 

 which will consistently and equably support it in all 

 directions ; whilst the latter involves the careful 

 infiltration of the specimen with, and its thorough 

 permeation by, a " mass " which, whilst warm, is 

 liquid, and which solidifies as it cools ; or, as in 

 the case of celloidin, the saturation of the specimen 

 with that substance, held in solution by ether, 



