10.2.
SUSPENDED AND FRAGMENTED MATERIAL
329
stages of drying. Often this can be effectively avoided by employing a
trick well known to the bacteriologists. A large drop with a high meniscus
is placed on the film with no expectation of allowing all of it to evaporate.
The drop is maintained for perhaps 30 seconds or even a few minutes
by the addition of more material if necessary. During this time some of
the particulate matter settles and becomes attached to the supporting
film. After a suitable time interval, as much fluid as possible is removed
with a bit of filter paper and then drying of the residual traces of the
fluid is permitted. One can expect that most of the suspended material
will be fairly uniformly distributed over the grid.
Once organic material has dried on a supporting film, there is little
likelihood of its washing off subsequently. Thus, one can employ "staining" procedures, histochemical reagents, or enzymatic digestions to such
screens before examining them in the electron microscope.
More quantitative methods of applying suspended material to prepared
grids involve "nebulizing" the suspension so that microdroplets of relatively constant size are formed. These, then, are allowed to settle upon the
supporting film. If the drops are truly minute, drying can be expected to
be almost instantaneous. If the concentration of suspended material is kept
within reasonable limits, particulate coalescence can be minimized or
avoided. Although some investigators have designed their own spray
equipment, a commercial device discovered by Hall (1956) has proved
particularly satisfactory. This equipment, manufactured by the Vaponefrin Co.,* is designed for creating an aerosol of aqueous medications
to provide symptomatic relief for bronchial asthma. The device has an
exterior wall which encloses an atmosphere, and also serves as the reservoir of the suspension. Squeezing a rubber bulb creates a fast moving
air stream through a nozzle inside of the container. Fluid introduced into
this no doubt is broken up at once. It is further nebulized as the stream
hits a baffle, which creates a cloud of truly minute droplets that immediately saturate the enclosed atmosphere. Any large droplets that escape
fragmentation fall back into the reservoir. Fine droplets stream out of
the relatively large exit with little velocity, and will settle down on grids
in its vicinity. Originally, the Vaponefrin Co. made this device in glass
which, of course, could be cleaned easily. Present models unfortunately
are manufactured out of plastic, apparently methacrylate, and thus must
be cleaned judiciously.
* Available from the Vaponefrin Co., 666 Fifth Ave., New York, New York.
SUSPENDED AND FRAGMENTED MATERIAL
329
stages of drying. Often this can be effectively avoided by employing a
trick well known to the bacteriologists. A large drop with a high meniscus
is placed on the film with no expectation of allowing all of it to evaporate.
The drop is maintained for perhaps 30 seconds or even a few minutes
by the addition of more material if necessary. During this time some of
the particulate matter settles and becomes attached to the supporting
film. After a suitable time interval, as much fluid as possible is removed
with a bit of filter paper and then drying of the residual traces of the
fluid is permitted. One can expect that most of the suspended material
will be fairly uniformly distributed over the grid.
Once organic material has dried on a supporting film, there is little
likelihood of its washing off subsequently. Thus, one can employ "staining" procedures, histochemical reagents, or enzymatic digestions to such
screens before examining them in the electron microscope.
More quantitative methods of applying suspended material to prepared
grids involve "nebulizing" the suspension so that microdroplets of relatively constant size are formed. These, then, are allowed to settle upon the
supporting film. If the drops are truly minute, drying can be expected to
be almost instantaneous. If the concentration of suspended material is kept
within reasonable limits, particulate coalescence can be minimized or
avoided. Although some investigators have designed their own spray
equipment, a commercial device discovered by Hall (1956) has proved
particularly satisfactory. This equipment, manufactured by the Vaponefrin Co.,* is designed for creating an aerosol of aqueous medications
to provide symptomatic relief for bronchial asthma. The device has an
exterior wall which encloses an atmosphere, and also serves as the reservoir of the suspension. Squeezing a rubber bulb creates a fast moving
air stream through a nozzle inside of the container. Fluid introduced into
this no doubt is broken up at once. It is further nebulized as the stream
hits a baffle, which creates a cloud of truly minute droplets that immediately saturate the enclosed atmosphere. Any large droplets that escape
fragmentation fall back into the reservoir. Fine droplets stream out of
the relatively large exit with little velocity, and will settle down on grids
in its vicinity. Originally, the Vaponefrin Co. made this device in glass
which, of course, could be cleaned easily. Present models unfortunately
are manufactured out of plastic, apparently methacrylate, and thus must
be cleaned judiciously.
* Available from the Vaponefrin Co., 666 Fifth Ave., New York, New York.