EMBEDDING 



mixtures of substances, are used for this purpose, of which soft 

 paraffin is perhaps the best. Samples of paraffin which vary in 

 hardness and melting point may be obtained from the dealers. 



The ordinary method of embedding is to make a cavity in a 

 piece of the substance sufficiently large to contain the object, 

 which, if fresh, must have been previously washed with alcohol 

 to remove all traces of water from its surface. If the object had 

 been previously preserved in alcohol, all superfluous fluid must 

 be removed from the surface with blotting-paper, but care must 

 be taken that the spirit which permeates the tissue shall not 

 evaporate. The object is then placed in the cavity, and with- 

 out unnecessary delay a small quantity of the embedding sub- 

 stance, melted over a spirit-lamp in a small tinned iron spoon, 

 is poured into the cavity so as to surround and cover the 

 object. 



If the object be small, it will be found convenient to heat one 

 end of a thick copper or platinum wire, and with it melt a small 

 cavity, in which the object may be placed in such position as 

 is found convenient. 



The sections must not be made until the paraffin is quite 

 cold, and firmly set. 



It is important to keep the embedded objects wet with 

 alcohol during the process of cutting, in order to prevent the 

 drying-up of the object, and its consequent contraction away 

 from the substance in which it is embedded. 



The sections when cut should be removed at once to a 

 watch-glass containing alcohol or water, by means of a camels'- 

 hair brush, or a jet of alcohol or water from a wash-bottle : the 

 thicker sections may then be removed, and the thinnest ones 

 selected for observation. 



V. Mounting Objects. Various specimens, whether sections 

 or objects which may be examined whole, require varied 

 treatment, and the common methods in ordinary use will be 

 described below, and illustrated by experimental exercises (see 

 pp. 17, &c.) ; meanwhile a few practical suggestions will be 

 given which are to be observed in all cases, whatever the 

 special method of treatment may be. 



I. Study to avoid all unnecessary manipulation of specimens ; 



