A METHOD FOR PREPARING PHOTOGRAPHS OF PETRI DISH CULTURES BY DIRECT CONTACT PRINTING ON PHOTOGRAPHIC PAPER
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A METHOD FOR PREPARING PHOTOGRAPHS OF PETRI
DISH CULTURES BY DIRECT CONTACT PRINTING
ON PHOTOGRAPHIC PAPER
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JOHN T. BUCHHOLZ AND I. M. LEWIS
I)epartment of Botany and Bacteriology, The University of Texas, Austin, Texas
Received for publication July 11, 1929
Recently we discovered that photographs of Petri dish cultures
prepared by direct contact printing on photographic developing
paper are as satisfactory for most purposes as pictures obtained
by the use of a camera and the usual method of photographic
technique. The Petri dishes are used in the same manner as
negatives and the resulting prints are positives, in natural size,
the colonies appearing as white objects on a black background.
The details of such forms as B. mycoides are reproduced with
striking clearness (fig. 1). Because of the simplicity of the
process, the excellence of the product and the many uses to which
it may be put by investigators and teachers, we have thought it
desirable to describe this method in some detail.
The entire process is carried out in a dark room, using a ceiling
lamp as a source or light for printing. At a distance of 2.5 to
3 meters the rays which reach the object, from a concentrated
source of light, are very nearly parallel and cast dark, sharp shad-
ows of the colonies on the white paper. We have used an
ordinary clear glass 150 watt Mazda lamp at 3 meters distance
from the object. A special opaque lamp shade is probably of no
great advantage, when the ceiling and walls are blackened, but
we have used a cylindrical shade painted black on the inside and
provided with a 60 mm. opening below in order to prevent re-
flections from the walls of the room. The light must be centered
directly above the exposing table so that the sides of the dish cast
no shadows.
All preliminary operations preceding the exposure may be
105106 JOHN T. BUCHHOLZ AND I. M. LEWIS
carried out by the use of conveniently placed ruby or amber
lights. The Petri dish, with cover removed, is placed bottom side
down on the sensitive side of the paper and pressed down. A
piece of cloth under the paper facilitates close contact which is
necessary. A special plate holder seems to be unnecessary.
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FIG. 1. PHOTOGRAPH OF A POURED DILUTION PLATE BY DIRECT CONTACT PRINTING
ON PAPER
When plate and paper are properly adjusted the ceiling -light is
turned on for the desired exposure. The period of exposure
depends on several factors and needs to be determined for each
culture. The color and transparency of the agar, its depth in the
dish, the kind of paper, the developer used, and the temperature
of development all influence the time required. With an agar
which is almost colorless, and with vigorous Novagas paper, thePHOTOGRAPHS OF PETRI DISH CULTURES 107
exposure may be as short as 10 seconds but with No. 4 Azo the
same subject may require 150 seconds. Agar or gelatin which
has more of the amber color, due to beef extract or beef infusion,
requires a longer exposure. We adjust the time of exposure so
that development of the print is completed in 35 to 60 seconds.
The kind of paper used is the most important single detail.
Bromide papers are too fast, requiring such short exposures
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(usually about 2 second) that there is difficulty in properly timing
the exposure, and they also lack contrast. If Azo paper is used it
should be No. 4 or No. 5; Nos. 1 and 2, in our experiments, always
gave unsatisfactory results; No. 3 may be useful for an unusual
subject. Excellent results were also obtained by using Gevaert's
Novagas vigorous paper. This paper has the advantage of re-
quiring a shorter period of exposure. Extra vigorous Novagas
was not tested but is probably still more desirable for very trans-
parent subjects. Both Novagas and Azo papers give satisfactory
detail and contrast.
The kind of developer appears to be of considerable importance.
The standard Eastman "MQ" Elon Hydrochinon developer is less
satisfactory than the Eastman Special, which may also be ob-
tained in tubes. We have tested several formulae and found the
following very satisfactory.
Formula D72. Stock solution
Water .
............................................. 500 cc.
Elon (Photol or Metol) .................................... 3 grams
Sodium sulphite ............................................. 45 grams
Hydrochinon ............................................. 12 grams
Sodium carbonate ......................................... 65 grams
Potassium bromide ......................................... 1.8 grams
Water to make ............................................. 1 liter
For use take 1 part stock solution to 1 part water.
Formula D78. Stock solution
Water .................................................. 500 cc.
Elon (Photol or Metol) .................................... 2.7 grams
Sodium sulphite ........................................... 40 grams
Hydrochinon ............................................. 10.6 grams
Sodium carbonate .......................................... 75 grams
Potassium bromide ........................................ .8 grams
Water to make ............................................ 1 liter108 JOHN T. BUCHHOLZ AND I. M. LEWIS
For use take 1 part stock solution to 2 parts water. Formula
D72 gives warmer tones and works faster than D73, but either of
these formulae will give good results. D73 diluted 1:2 seems to
TABLE 1
Exposure and development time table for an average subject with various brands of
paper and kinds of developer
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The source of lighJt was a clear glass 150 watt Mazda Lamp at a distance of 3
meters. Time is given in seconds.
AZO NO. 6
AZO NO. 3
AZO NO.Z4
GUVAURY's
NOVAGAS BROMIDE
OR
RECOM- DECom- INFIOR (VIGOROUS) (NOT RZCOx.
MENDED MEDXD FOR OUR DCOR- MEDMD)
SUBJECTS M DENDD
_~~~~~~~4
14
Eastman Special 75- 90 40 150 50 30 40 30 25 j? 180
760F. recommended 15 45
10 60
Eastman Formula D72 120 40 150 50
Diluted 1:1 77°F. 105 50
recommended 90 65
Eastman "MQ" Elon- 210 25 300 35 25
Hydro. not recom- 180 40 240 45 60 35
mended 150 70 180 90 30 50
Azo No. 2
RIORi NOT RE-
COMEXDED
Eastman Formula D73 240 30 360 25 180 30
full strength stock 180 45 300 45 120 45
solution 77°F. 120 60 240 55 90 90
Eastman Formula D73 180 35
diluted 1:2 parts 150 45
water 77°F. 120 60
90 90
work faster than the stock solution. For a convenient quickly
prepared developer we recommend Eastman's Special. Table 1
showing the periods of exposure and development required to givePHOTOGRAPHS OF PETRI DISH CULTURES 109
satisfactory results, using the several brands and grades of paper
and kinds of developer which we have tested, suffices to indicate
the time relations to be expected for an average subject.
The Petri dishes for cultures which are to be photographed
should be selected with care. They should have flat bottoms,
free from scratches and other imperfections. Care should be
exercised to see that the layer of agar is not too deep and that its
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thickness is uniform throughout.
Sensitized plates or films may be used in the same manner as
paper if desired. Since these have a bromide emulsion they must
be handled only in ruby light, and their time of exposure is very
short, only a fraction of a second, with a less powerful ceiling
lamp. A slow emulsion is preferable. We have used Eastman's
Process films, developed with a contrast developer (Dll), with
very satisfactory results. The time of development may be va-
ried in order to give different degrees of contrast. These films
give positives in the same sense as the contact prints described
above, and the prints made from them are reversed, black colonies
against a white background. If white colonies against a black
background are desired from such films, it is necessary to print
the film image in a printing frame on another film which is devel-
oped and used as a negative for the final prints. When films are
used in making the first impression, the differences due to the
variations in the thickness of the agar in various parts of the Petri
dish are less pronounced. Otherwise the use of films offers no
great advantages. The accompanying illustration (fig. 1) of a soil
dilution plate was prepared by direct contact printing on Azo
paper No. 4.
A survey of the literature revealed the fact that others have
employed methods similar to the one developed in our work but
differing from it in certain important details. De Giaxa (1888)
appears to have been the first worker to describe a direct printing
method for this purpose. At this early date the original Koch
plates were still in use. He placed such a plate on a piece of sen-
sitized printing out paper, exposed to sunlight, and then treated
the print according to the toning and fixing methods in use at that
time. The illustration which accompanies his description of the110 JOHN T. BUCHHOLZ AND I. M. LEWIS
process is remarkable for the differentiation and contrast which it
shows. De Giaxa pointed out the advantages of such a method
and the principles involved in the -process, but the method does
not appear to have come into general use, if one may judge by the
published work which followed.
Lindner (1914) described a photographic method based on a
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process of, shadow printing, using various biological objects
placed directly on photographic paper. He employed an arc
lamp and mirror, describing the parallel rays as an essential
condition of his process. The Petri dish cultures which he has
illustrated show the usual white colonies against a dark back-
ground. In a more extensive treatise (1920) this author en-
larges on the general subject of photography without the use of a
camera, but this book has not found its way into many American
libraries.
Broadhurst (1917) described a method of printing from agar
plates directly on blue-print paper. She called attention to the
simplicity of the process and its usefulness in the preparation of
demonstration material for teachers of bacteriology. Since blue-
prints are not suitable for reproduction, illustrations of this
method are lacking. It is possible that others may have de-
scribed a similar procedure but if so we have not found reference
to it in a search of the literature.
The method which we have employed appears to be more simple
than any which we have seen described. We have used it for the
reproduction of many types of Petri dish cultures including expo-
sure plates; water, milk and soil analyses; effect of light, disinfec-
tants and dyes; bacterial antagonism; liquefaction of gelatin and
effect of bacteria on gelatin in Frazier's medium. The method is
admirably suited to the needs of students who wish to preserve
results obtained in class work. Students who have had no pre-
vious experience with photography have been able, by this method,
to obtain excellent illustrations of plates prepared in routine
laboratory experiments. We believe the method will be found
very useful by teachers of bacteriology.PHOTOGRAPHS OF PETRI DISH CULTURES 111
REFERENCES
BROADHURST, JEAN 1917 Blue printing directly from agar plates. Jour. Bact.,
3, 187.
DE GIAXA 1888 Ueber eine einfache Methode zur Reproduction der Koch-
schenplatten. Centralblatt fur Bakteriologie etc., 3, 700.
LINDNER, P. 1914 Ein einfaches photographisches Verfahren in Dienste der
biologischen Analyse. Wochenschr. f. Brauer., 31, 87.
LINDNER, P. 1920 Photographie ohne Kamera. Die Photographische Bibli-
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