THEORY OF IMBEDDING

1 thin slices cut from the mass all the details of structure will
precisely retain their natural relations of position. Such a
process of imbedding is at the same time practically a process
of hardening in so far as it enables us to give to tissues a
degree of firmness that could otherwise only be obtained by
the employment of chemical processes such as prolonged
treatment with chromic acid and the like.
The principle of the methods of this second class is either,
(a  like that of the first, that by immersion of the object to be
cut in some material that is liquid while warm 'and solid
r1o  when cold, all the parts of the object may be duly surrounded
spass  by the supporting mass (the second class differing from   the
first chiefly in the employment of materials possessing greater
Thd  power of penetration whilst liquid, in longer immersion in the
e Sd  liquid mass, and in such previous preparation of the object,
hN ot  by soaking in some liquid that is a solvent of the imbedding
al  material, as makes it more readily susceptible of infiltration
mayk  by the latter) ; or the processes may be based on another prin-
h6 is  ciple, namely that of the employment of substances which
ud in  whilst in solution are sufficiently fluid to penetrate the object
aiegthe  to be imbedded, whilst at the same time after the evaporation
rias  or removal by other means of their solvent, they acquire and
ati  impart to the imbedded object sufficient firmness for the pur-
)tIM is  pose of cutting. The collodion process sufficiently exemplifies
deb  this principle. If a piece of soft tissue be dehydrated, and
or ii.  soaked first in ether and then in collodion, and if the ether
rio the  contained in the collodion be allowed slowly to evaporate, the
order  tissue and surrounding mass of collodion will acquire a con-
aLh in  sistency such as to admit of thin sections being cut from
r, it is  them.
Iveah  The egg-emulsion process, in which a mass that is liquid
present whilst cold is coagulated by heat, forms a class by itself.
r other  In any of these cases the material used for imbedding is
sistenlc  technically termed an  " imbedding-mass."    (Einbettungs-
il the masse :-masse d'inclusion. Imbedding methods are spoken

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