4.2.
DEHYDRATION
85
each) followed by a longer one (15-20 minutes). Only then is the tissue
passed on. As the next section (Chapter 4.3) indicates, it is usually
desirable to employ an intermediate solvent between the dehydrant
and the embedment (the principal exception is methacrylate). Thus it
is only after this additional step that the tissue is exposed to a graded
series of solvent and plastic mixtures. In our own laboratory we routinely
use a platform shaker to facilitate fluid exchange at all stages of dehydration, as well as during fixation and infiltration. The added effort is
negligible, and is excellent insurance of a standardized result.
Care should be taken that the container and, particularly, its cork
or lid do not retain traces of water which eventually would contaminate
the plastic mixture.
There seems to be no harm in storing tissue indefinitely in 95% alcohol, or in an intermediate solvent, before blocking it, should this be
convenient.
From time to time agents other than ethyl alcohol have been proposed for dehydration. Acetone has been recommended by several investigators, yet in this writer's experience severe specimen damage from
incomplete dehydration is a danger, and it is suggested that it be used
cautiously if at all. The difficulty lies in getting and keeping anhydrous
acetone. However, with the advent of suitable "molecular sieves," water
can be more reliably eliminated from organic fluids than formerly was
possible by the use of anhydrous salts. Linde, type 4A pellets or granules
are designed particularly for this purpose. They are manufactured by
the Linde Air Products Co., a Division of the Union Carbide and Carbon
Corp., New York, New York, and are commonly available through local
chemical supply houses.
Other dehydrating agents include dioxane which this writer has some
reason to distrust. In addition he has tried Cellosolve (monomethyl
ether of ethylene glycol) and dimethyl formamide. These latter substances did not seem to damage specimens, but offered no obvious advantages over ethyl alcohol. Both dioxane and dimethyl formamide are
somewhat dangerous to handle.
It has been suggested that methyl alcohol be used as a dehydrating
agent, apparently because of its lesser solvent action. Although this writer
has not had experience with it, it seems unlikely that there is an important advantage.
The small size of tissue specimens makes it impractical to move them
from one bath to another. Instead, fluids should be poured out of the
DEHYDRATION
85
each) followed by a longer one (15-20 minutes). Only then is the tissue
passed on. As the next section (Chapter 4.3) indicates, it is usually
desirable to employ an intermediate solvent between the dehydrant
and the embedment (the principal exception is methacrylate). Thus it
is only after this additional step that the tissue is exposed to a graded
series of solvent and plastic mixtures. In our own laboratory we routinely
use a platform shaker to facilitate fluid exchange at all stages of dehydration, as well as during fixation and infiltration. The added effort is
negligible, and is excellent insurance of a standardized result.
Care should be taken that the container and, particularly, its cork
or lid do not retain traces of water which eventually would contaminate
the plastic mixture.
There seems to be no harm in storing tissue indefinitely in 95% alcohol, or in an intermediate solvent, before blocking it, should this be
convenient.
From time to time agents other than ethyl alcohol have been proposed for dehydration. Acetone has been recommended by several investigators, yet in this writer's experience severe specimen damage from
incomplete dehydration is a danger, and it is suggested that it be used
cautiously if at all. The difficulty lies in getting and keeping anhydrous
acetone. However, with the advent of suitable "molecular sieves," water
can be more reliably eliminated from organic fluids than formerly was
possible by the use of anhydrous salts. Linde, type 4A pellets or granules
are designed particularly for this purpose. They are manufactured by
the Linde Air Products Co., a Division of the Union Carbide and Carbon
Corp., New York, New York, and are commonly available through local
chemical supply houses.
Other dehydrating agents include dioxane which this writer has some
reason to distrust. In addition he has tried Cellosolve (monomethyl
ether of ethylene glycol) and dimethyl formamide. These latter substances did not seem to damage specimens, but offered no obvious advantages over ethyl alcohol. Both dioxane and dimethyl formamide are
somewhat dangerous to handle.
It has been suggested that methyl alcohol be used as a dehydrating
agent, apparently because of its lesser solvent action. Although this writer
has not had experience with it, it seems unlikely that there is an important advantage.
The small size of tissue specimens makes it impractical to move them
from one bath to another. Instead, fluids should be poured out of the