7.12.
AUTORADIOGRAPHY
253
If emulsion is to be spread over sections by dipping and draining, the
viscosity of the emulsion must be carefully controlled to produce a uniform film of reproducible and appropriate thickness. Hay and Revel
(1963) dilute Ilford L-4 emulsion 7-8 times with distilled water, and use
the emulsion at 45 °C. Ordinary microscope slides can be used as convenient carriers for specimen grids. Holes slightly smaller than grids
are punched in strips of double-surfaced adhesive tape. The tape is then
fastened to the glass slide, and grids mounted over the holes by pressing
their edges into the sticky edges of punched holes. Then the slides are
dipped in the warm dilute emulsion, drained vertically, and allowed to
dry at room temperature. Finally, they are placed in light-tight boxes
and stored in a refrigerator for the several weeks necessary to expose the
emulsion. Obviously it is advisable to test the emulsion for background
grain before each use. Thus a blank slide should be dipped, dried, developed, and examined in the light microscope before experimental material
is coated. It is recommended that the emulsion be discarded if the test
shows more than 10 background grains per oil immersion field. More
primitive versions of this method of applying emulsion to grids include
simply touching a grid surface (section side down) to diluted emulsion
and then draining it on filter paper, or placing a drop of emulsion on
the surface, letting it stand for a few moments, and then removing the
excess with a bit of filter paper.
Details of a method of preparing uniform gelled emulsion films which
are secondarily applied to grids are described by Caro and van Tubergen
(1962). They dilute 10 gm of Ilford L-4 emulsion with 20 ml of distilled
water, and warm this for 15 minutes at 45°C. After thorough stirring, the
beaker is placed in an ice bath for 2-3 minutes, and then returned to
room temperature for 30 minutes at which time the emulsion should
be very viscous. A loop of thin wire, 4 cm in diameter, is dipped into
it and withdrawn slowly, forming a thin film spanning the loop. The film
should gel almost immediately. If it does not, presumably the emulsion
was not chilled sufficiently in the ice bath. The loop with a solid film
then is touched to the surface of a glass slide upon which a number of
grids have been laid with mounted sections up. The film falls on the
grids and over the sections and adheres to them firmly. Certainly a film
prepared in this way can be expected to be reasonably uniform and quite
adequate for routine work. However, Caro and van Tubergen have
worked out a much more elaborate method of preparing a particularly
AUTORADIOGRAPHY
253
If emulsion is to be spread over sections by dipping and draining, the
viscosity of the emulsion must be carefully controlled to produce a uniform film of reproducible and appropriate thickness. Hay and Revel
(1963) dilute Ilford L-4 emulsion 7-8 times with distilled water, and use
the emulsion at 45 °C. Ordinary microscope slides can be used as convenient carriers for specimen grids. Holes slightly smaller than grids
are punched in strips of double-surfaced adhesive tape. The tape is then
fastened to the glass slide, and grids mounted over the holes by pressing
their edges into the sticky edges of punched holes. Then the slides are
dipped in the warm dilute emulsion, drained vertically, and allowed to
dry at room temperature. Finally, they are placed in light-tight boxes
and stored in a refrigerator for the several weeks necessary to expose the
emulsion. Obviously it is advisable to test the emulsion for background
grain before each use. Thus a blank slide should be dipped, dried, developed, and examined in the light microscope before experimental material
is coated. It is recommended that the emulsion be discarded if the test
shows more than 10 background grains per oil immersion field. More
primitive versions of this method of applying emulsion to grids include
simply touching a grid surface (section side down) to diluted emulsion
and then draining it on filter paper, or placing a drop of emulsion on
the surface, letting it stand for a few moments, and then removing the
excess with a bit of filter paper.
Details of a method of preparing uniform gelled emulsion films which
are secondarily applied to grids are described by Caro and van Tubergen
(1962). They dilute 10 gm of Ilford L-4 emulsion with 20 ml of distilled
water, and warm this for 15 minutes at 45°C. After thorough stirring, the
beaker is placed in an ice bath for 2-3 minutes, and then returned to
room temperature for 30 minutes at which time the emulsion should
be very viscous. A loop of thin wire, 4 cm in diameter, is dipped into
it and withdrawn slowly, forming a thin film spanning the loop. The film
should gel almost immediately. If it does not, presumably the emulsion
was not chilled sufficiently in the ice bath. The loop with a solid film
then is touched to the surface of a glass slide upon which a number of
grids have been laid with mounted sections up. The film falls on the
grids and over the sections and adheres to them firmly. Certainly a film
prepared in this way can be expected to be reasonably uniform and quite
adequate for routine work. However, Caro and van Tubergen have
worked out a much more elaborate method of preparing a particularly