11.4.
SPECIMEN PREPARATION
349
8.6 and a 78% water solubility. He indicates, however, that he has had
difficulty using it with biological objects, "perhaps because of its reactivity."
Reactivity with biological materials also will limit the use of mercuric
salts in potassium iodide. These have been suggested by S. J. Holt who
indicated that such compounds can be formed easily by adding just
enough of a solution of the latter to a solution of the former to dissolve
the precipitate that is formed at first. The density of these compounds is
not appreciably better than that of sodium phosphotungstate, however.
11.4. Specimen Preparation for Negative Staining
The techniques developed for fragmenting, dispersing, and suspending
biological products are in general adaptable to negative staining procedures. Specimens are deposited on previously prepared supporting films
either by the single drop transfer method, or by spraying microdroplets,
as described in Chapter 10.2. The specimen particles may be deposited
either in advance of applying the stain (in which case a single drop of
stain is subsequently added and allowed to dry), or, commonly, the
specimen particles are mixed with the stain and deposited together.
Huxley (1962) has pioneered what may be termed protein chemistry
performed on the microscope grid previous to staining. Thus, "pure"
proteins are deposited on the grid membrane in appropriate quantities.
He does this by putting a drop of the protein solution on the grid film
and then allowing it to stand for a brief period before blotting the
excess fluid. He finds that seconds rather than minutes are all that is
required to attach particles to the grid films. Once attached, however,
the particles will not come off unless they are dissolved or digested by
subsequent treatments. Thus, successive reactions can be performed upon
the specimen. The specimen can be kept wet throughout all changes of
solution if this is desirable. It is only when one is through with the
experimental procedures that stain is added and a dry preparation
obtained for the microscope. In the meanwhile, solubilities might have
been studied under a variety of conditions, or enzymatic or serological
reactions performed.
Ordinarily it is desirable that surface active material be present when
stain is applied. This is important in filling such interstices as may be
SPECIMEN PREPARATION
349
8.6 and a 78% water solubility. He indicates, however, that he has had
difficulty using it with biological objects, "perhaps because of its reactivity."
Reactivity with biological materials also will limit the use of mercuric
salts in potassium iodide. These have been suggested by S. J. Holt who
indicated that such compounds can be formed easily by adding just
enough of a solution of the latter to a solution of the former to dissolve
the precipitate that is formed at first. The density of these compounds is
not appreciably better than that of sodium phosphotungstate, however.
11.4. Specimen Preparation for Negative Staining
The techniques developed for fragmenting, dispersing, and suspending
biological products are in general adaptable to negative staining procedures. Specimens are deposited on previously prepared supporting films
either by the single drop transfer method, or by spraying microdroplets,
as described in Chapter 10.2. The specimen particles may be deposited
either in advance of applying the stain (in which case a single drop of
stain is subsequently added and allowed to dry), or, commonly, the
specimen particles are mixed with the stain and deposited together.
Huxley (1962) has pioneered what may be termed protein chemistry
performed on the microscope grid previous to staining. Thus, "pure"
proteins are deposited on the grid membrane in appropriate quantities.
He does this by putting a drop of the protein solution on the grid film
and then allowing it to stand for a brief period before blotting the
excess fluid. He finds that seconds rather than minutes are all that is
required to attach particles to the grid films. Once attached, however,
the particles will not come off unless they are dissolved or digested by
subsequent treatments. Thus, successive reactions can be performed upon
the specimen. The specimen can be kept wet throughout all changes of
solution if this is desirable. It is only when one is through with the
experimental procedures that stain is added and a dry preparation
obtained for the microscope. In the meanwhile, solubilities might have
been studied under a variety of conditions, or enzymatic or serological
reactions performed.
Ordinarily it is desirable that surface active material be present when
stain is applied. This is important in filling such interstices as may be