Apparatus for analyzing and evaluating tests in a plurality of wells

An apparatus is described with which a plurality of microbiological tests made in wells located in a pattern of rows on a tray can be conveniently analyzed and evaluated. A housing is formed with a tray analysis section and over which an arm is mounted to move from row to row. A plurality of manually activated signal generators are mounted on the arm, with the generators being aligned with a well in a row to enable the operator, upon identification of a particular well in a row as representative of analysis, to actuate the signal generator in registration therewith. The signals are representative of a score value and are recorded on score forms located in a test scoring section over which the arm moves with recording elements, also mounted on the arm. An elongated illuminator for a row of wells is described and which is conveniently adjusted to view selected test wells against different background lighting. The apparatus is particularly effective in color analysis of test wells by use of an apertured mask having color markings adjacent corresponding well locations.

FIELD OF THE INVENTION 
This invention relates to an apparatus for visual analysis of tests such as 
turbidometric and/or colorimetric tests. More specifically, this invention 
relates to an apparatus for analyzing and evaluating microbiological tests 
made in a plurality of wells located in a tray. 
BACKGROUND OF THE INVENTION 
Microbiological tests for the identification and/or counting of organisms 
have been developed. Such tests are commonly performed in laboratories in 
hospitals and medical clinics and the like. In one such known test, a 
minimum inhibiting concentration (MIC) is obtained by exposing an organism 
to different dilutions of an antibiotic and analyzing which dilution level 
is sufficient to kill and/or inhibit growth the organism. 
Such MIC test is commonly done in a tray containing a regular pattern of 
small wells usually arranged in rows and columns. In one such tray, for 
example, there may be twelve rows and seven columns of wells for a total 
of 84 wells. Other trays may have a different number of wells. Each row of 
wells may contain different antibiotic in dilutions which are typically 
graded with scores in levels of the power of two, e.g. 1, 2, 4, 8, 16, 32 
and 64, or some other sequence of numbers. 
A technician commences such MIC test by employing a tray in which the wells 
contain antibiotics with progressive concentrations and then adds a growth 
solution containing the organism in each of the wells. After an incubation 
period, the technician visually analyzes the wells to determine at which 
antibiotic concentration (the MIC) the organism appears to have been 
killed and/or growth inhibited. This analysis is done visually by scanning 
a row of wells containing a particular antibiotic and noting in which well 
the solution appears, for example, cloudy, opaque or clear. The technician 
does this analysis for each row and assigns a score value to his analysis 
by noting on a corresponding form carrying score value notations which 
well in the row contained the minimum inhibitory concentration. 
The trays of wells usually are transparent so that the technician may 
observe the test wells against a light or dark background. In other 
microbiological tests the tray may include in some of the wells various 
components which, when innoculated with the specimen solution, react with 
certain organisms in a particular manner. These wells, when analyzed and 
appropriately evaluated by the technician, provide an identification of 
the organism. 
In a typical laboratory environment a large number of such organism 
analyses must be performed. This often results in a fatigue of the 
technician who has to constantly look at tiny test wells and becomes prone 
to note the wrong score value on the score form and would welcome a 
procedure which would simplify the analysis and evaluation with less 
chance for error and with greater speed. 
SUMMARY OF THE INVENTION 
With an apparatus in accordance with the invention, the analysis and 
evaluation of tests made in a plurality of wells arranged in a pattern of 
rows on a tray can be made accurately and conveniently. As described 
herein with reference to one form for an apparatus in accordance with the 
invention, a housing is provided with its top surface formed into a test 
analysis section sized to receive a tray having a plurality of test 
containing wells. An arm is mounted to the housing to move over its top 
surface and align a reference edge of the arm along rows of wells. The arm 
carries a plurality of score signal generators which are respectively 
located for visual registration with a different well in a row of wells of 
a tray placed in the test analysis section. 
As the arm is moved across the top surface of the housing and the arm's 
reference edge is successively aligned with a row of test wells, the 
technician makes a visual analysis of the tests and selects a well in the 
row by actuating a score signal generator which is in registration with 
the selected well. The score signals associated with the various rows then 
conveniently represent an evaluation of the tests in the rows and may be 
used to make a record of the analysis. The record may be a visual notation 
on a form or stored in a magnetic medium or the memory of a signal 
processor. 
With an apparatus in accordance with the invention, a tray carrying a 
plurality of microbiological test wells can be accurately and conveniently 
analyzed and evaluated. As described herein for one form of the invention, 
an apparatus is provided with a tray receiving section and arm as 
described and also a test scoring section shaped to receive a score form. 
The score form has score value notations located thereon in corresponding 
spatial relationship with the location of wells on a tray. The score value 
locations are so spaced that as the reference edge of the arm is aligned 
with rows of test wells, a corresponding row of score value locations is 
spaced below the arm and operatively aligned with actuators for producing 
a visual notation in response to a score signal. 
A rapid and accurate analysis of a tray of test wells can be conveniently 
made while their evaluation can be simultaneously accurately recorded as 
the arm is moved to successive positions aligned with a row of wells on a 
tray. The technician's access to score signal generators is visually 
effective to accurately identify each well representative of the analysis, 
while simultaneously and accurately obtaining a physical record of the 
analysis. 
The arm is provided as described for a preferred form of the invention, 
with a row of recording elements which are so aligned with the score 
signal generators as to mark a notation on the score form at the proper 
location. An adjustable shutter assembly is mounted to the arm to move 
therewith inside the housing below the top surface. The shutter assembly 
is located below the tray receiving section to control background 
illumination for a group of wells in a tray depending upon the type of 
background light needed for a visual analysis of the tests in the wells. 
The arm has a closed loop shape composed of upper and lower segments 
located respectively above and below the top surface of the housing. The 
upper arm segment serves to provide an accurate visual reference edge for 
alignment of the arm with a row of wells as well as carry manually 
actuated score signal generators. The lower arm segment supports the 
background shutter assembly, electrical controls and actuators for 
producing the markings on a score form in response to a score signal. 
With such arm construction, the upper segment overlying the housing with 
the tray analysis and test scoring sections contributes with its shape, 
its alignment with test wells and convenience in generating score signals 
to a more consistent accuracy in the analysis and evaluation by a 
technician. 
Such improvement in the analysis of test wells can be particularly 
appreciated when a visual color analysis of test wells is required. In 
such case as described herein for one form of the invention, a mask is 
provided to overly the tray analysis section but below the arm. The mask 
has a transparent section, such as formed by a cut-away aperture, and 
which is shaped to visually reveal certain wells of an underlying tray. On 
the mask and adjacent the transparent section are color indications to aid 
the technician in the visual color identification of the tests in 
adjacently located wells. Score signals are generated as a result of the 
technician's analysis of the test well whose color most closely matches a 
particular color value. As further described herein, the shutter assembly 
is shaped to provide the desired background illumination below the test 
wells to enhance such color identification. 
It is, therefore, an object of the invention to provide an apparatus for 
analyzing and evaluating test wells arranged in rows in a tray. It is a 
further object of the invention to provide such apparatus which is 
convenient to use, enhances the accuracy of the visual analysis and 
conveniently provides score signals representative of an evaluation of the 
visual analysis. It is a still further object of the invention to provide 
an apparatus with which the analysis of microbiological tests performed in 
a plurality of wells in a tray can be conveniently analyzed and accurately 
evaluated. 
These and other objects and advantages of the invention can be understood 
from the following description of a test analysis and evaluating apparatus 
described in conjunction with the drawings.

DETAILED DESCRIPTION OF DRAWINGS 
With reference to FIG. 1, an apparatus 20 in accordance with the invention 
is shown formed of a housing 22 with a top surface 24 formed into a test 
analysis section 26 and a test scoring section 28. 
An arm 30 is shown spaced from and suspended over top surface 24 and is 
supported inside housing 22 for movement along the top surface 24 in the 
direction indicated by arrow 32. The arm 30 is formed of an upper segment 
34 and lower segment 36 located inside housing 22. The arm is supported 
inside housing 22 and extends through slots 38, 40 (only one slot being 
visible in the view of FIG. 1). 
The test analysis section 26 is formed in a recess 42 below a platform 44 
of top surface 24 and is sized to receive a tray containing a plurality of 
wells arranged in rows and columns as will be further explained. The test 
section has an extended aperture 46 in the wall 48 of top surface 24 and 
reveals a test well illuminating and shutter assembly 50 mounted to the 
lower segment 36 of arm 30. The assembly 50 provides a controlled 
illumination of a group of test wells through a slot 52 aligned below and 
in front of a reference edge 54 of upper segment 34 of arm 30. 
Control over the background of slot 52 and thus a row of wells is provided 
with a shutter lever 56 which laterally extends through a slot 58 in arm 
30. The shutter lever 56 is formed of a spring element biased to move into 
either of three control notches 60.1, 60.2 and 60.3, respectively 
representative of a white, mixed, or all black background. 
Recess 42 has a bottom wall 62 surrounding aperture 46 to support a tray 
which seats against an end wall 64 and freely fits, but with little 
clearance, between side walls 66, 68. End wall 64 is so located that 
reference edge 54 on arm 30 may be moved to successive indent positions in 
alignment with rows of wells on a tray. 
Arm 30 is provided with a plurality of score signal generators 70 in the 
form of push button switches. The switches 70 are shown in the view of 
FIG. 1 as formed of a pair of spring conductors 72, 74, the upper 72 of 
which may be depressed by an operator. Preferably, switches 70 are of 
membrane form as will be further described with reference to FIGS. 8 and 
9. Switches 70 are spaced on arm 30 in a predetermined manner for 
registration with a well in a row of wells in a tray and when actuated, 
generate a score signal representative of an evaluation of a visual 
analysis of test wells located in the test analysis section 26. 
The test scoring section 28 is formed with a recess 80 having a bottom 82, 
end wall 84 and side walls 86, 88. Bottom 82 has a plurality of 
longitudinal parallel slots 90 sized to receive from inside housing and 
below bottom 82 arm mounted recording elements 92 for making a notation on 
a score form in coooperation with anvils 94 mounted to arm 30 over test 
scoring section 28. The shape of the notation may vary as desired, 
depending upon the shape of anvil 94. Thus an arrow, dot, dash or other 
mark may be used and is placed adjacent a printed score value to indicate 
the analysis and evaluation made by the technician of the corresponding 
row of test wells 104. 
A spring loaded, pivotly mounted retainer 96 is shown located near end wall 
84 to maintain a score form in registration with the test analysis 
section. A pivotly mounted cover 98 is provided to protect internal 
devices in the housing 22. 
With the arm 30 being movable over the housing top surface 24, a technician 
may conveniently align the arm with successive rows of wells for analysis 
and evaluation. This may be particularly appreciated with reference to 
FIG. 2. In this figure a tray 100 having a plurality of test wells 102 is 
shown placed in test analysis section 26 below arm 30. The tray 100 is 
formed of a transparent plastic material and has a total of eighty-four 
wells 102 arranged in a regular rectangular pattern of twelve rows 104 and 
seven columns 106. 
Although the use of trays with a plurality of test wells is well known for 
use in microbiological tests, the particular tray 100 and test analysis 
section 26 are shaped to place the tray 100 with particular alignment 
relative to arm 30 and test scoring section 28. A tray alignment 
projection 108 is shown on top surface 24 of housing 22 and aids in 
precisely locating and retaining a tray 100 in the desired aligned 
position in test analysis section 26. 
With the placement of a tray 100 in test analysis section 26, the well 
columns 106 are in registration with the score signal generators 70 as 
shown. 
The test scoring section 28 is sized and shaped to receive a score form 120 
on which there are rows 122 of score locations 124 respectively in 
correspondent locations with respect to the rows 104 and individual wells 
106 in a tray 100. The spacing between score location rows 122 is made the 
same as between test well rows 104. In this manner, as the reference edge 
54 of arm 30 is aligned just below a row of wells, such as 104.2, the 
recording elements 92 are in registration with score locations 124 in a 
row 122.2 on score form 120. 
The score form 120 may be a single sheet, but preferably is made up of 
multiple sheets with identical notations and each sheet provided with an 
ink carrying material which, upon application of pressure form a print 
element, will form a character. The score form may have such appearance 
and carry notations as is appropriate for the type of tests contained in 
the wells 102 in tray 100. For example, the sixth test well row 104.6 in 
tray 100 may contain tetracycline in varying concentrations as represented 
by the score value numbers noted in the corresponding row 122.6 on score 
form 120. Other test well rows may contain different materials, some of 
which are noted on the form 120, such as tobramycin, cephalothin, 
carbenicillin and others which are not indicated to preserve clarity of 
the drawing. 
The score form 120 is so designed that the score locations 124, as denoted 
by small marks adjacent the concentration numbers, are in registration 
with the recording elements 92 when the associated row 104 of test wells 
102 is aligned with reference edge 54 of arm 30. In the embodiment as 
shown, this is obtained by sizing form 120 in such manner that when its 
top edge 126 is in abutment with the end wall, 84, the desired 
registration is obtained. The distance, d, between end walls 64 and 84 is, 
therefore, known and selected to provide score form 120 with sufficient 
space above the first row 122.1 for entry of information such as patient 
identification, etc. while also enabling use of a straight ruler shape for 
upper segment 34 of arm 30. 
Arm 30 is provided with successive stable index positions, which coincide 
with the alignment of reference edge 54 with the various rows 104 of wells 
102. This is obtained with an indent mechanism 130 (see FIG. 7) operative 
on the lower segment 36 of arm 30 and inside housing 22. 
In the operation of apparatus 20, the technician aligns reference edge 54 
just below a row 104 of test wells 102, by which arm 30 is automatically 
operatively registered with a corresponding row 122.2 of score locations 
124 on score form 120. As the technician makes a visual analysis of the 
wells in row 104.2, the one well 102 representative of a particular test 
condition, such as a transition from cloudy to clear, is identified and 
the appropriately registered score signal generating switch 70 actuated. 
This in turn causes the actuation of a corresponding recording element 92 
in test scoring section 28 and thus form a notation on score form 120 at 
the proper score location 124. 
The technician may thus advantageously concentrate his attention to the 
test analysis section 26 and assure proper registration with the 
appropriate row 104 of test wells and the visual analysis of that row 
without concern of the accuracy of the transfer of the visual analysis to 
the score form 120. This transfer is automatically assured by the 
actuation of the proper switch, which by its visual registration with a 
well 102 in a row 104 and close proximity thereto facilitates in a rapid 
and accurate transfer and thus evaluation of the technician's visual 
analysis. 
Although the spacings between adjacent rows 122 is the same as between test 
well rows 104 on a tray 100, the lateral spacing between columns of score 
locations 124 may vary depending upon lateral spacing of recording 
elements 94 and desired width for forms 120. The lateral edges 128.1 and 
128.2 of a score form 120 are preferably closely spaced to side walls 86, 
88 of test scoring section 28 while still enabling free clearance fit 
between the form and the side walls 86, 88. 
In the tray 100 there are seven columns 106 of test wells 102, yet there 
are eight score signal generators, with the extreme right one, 70.8, which 
is not in registration with any test well 102, being used when, for 
example, none of the antibiotic concentrations in the row of test wells 
can be used in the analysis. In such case the score signal generator 70.8 
is actuated to correspondingly cause the extreme right recording element 
92.8 to record a notation at score location 124.8. 
In the embodiment of FIG. 3, the apparatus 20 is employed to analyze a tray 
100.1 containing an arrangement of microbiological tests different from 
those employed in the tray 100 in FIG. 2. Tray 100.1 has the first two 
columns 106.1 and 106.2 of test wells 102 filled with compounds which, in 
response to certain organisms, develop different colorations. The 
technician must visually analyze these colors. 
Apparatus 20 is particularly well suited in such color analysis by 
employing a mask overlay 140 with alignment holes 142 sized to receive 
alignment pins 144 (see FIG. 2) projecting from top surface 24 of housing 
22. Mask 140 is provided with a transparent aperture 146, in the form of a 
cut-out, located to reveal test well columns 106.1 and 106.2 of the 
underlying tray 100.1. In the particular embodiment of FIG. 3, the 
aperture 146 is shaped to reveal only certain test wells in the columns as 
shown. The mask 140 rests on top surface 24 but is located below the arm 
30 which is free to move over the mask 140. 
Since the revealed test wells 102 are examined as to color, mask 140 is 
provided adjacent the test wells with appropriately colored markings 148 
to aid the technician in identifying the well having a similar color, 
depending upon the test being made in the well. This is particularly 
effective in aiding the technician in making a visual color comparison 
analysis. The proximity of the color markings 148 to the revealed test 
wells facilitates these comparisons. The visual alignment of the switches 
70 with a well in the columns 106.1 and 106.2 further assures appropriate 
marking of a score form 150 located in the test scoring section 28. 
The mask 140 is shown with a single transparent aperture; however, mask 140 
may be provided with a plurality of apertures arranged to overly the 
appropriate test wells while the color markings 148 are closely spaced to 
the respective apertures. The color markings 148 may take such shape as 
appears to be visually effective in aiding the technician's color 
analysis. 
Score form 150 has the same width and rows 122 of score value locations as 
score form 120 in FIG. 2 so that score notations can be made with the 
recording elements 92 (see FIG. 2). In the view of FIG. 3, only the anvils 
94 are being shown in dashed lines. The score forms 120, 150 need not have 
the same length; however, the first row 122.1 of score values should be 
spaced the proper distance from edge 126 to assure correct registration 
with rows 104 in the tray 100.1. 
Color valuations are recorded on score form 150 with a score value location 
such as denoted at 152 within vertically oriented line enclosed segments 
154. These score value segments 154 are used to aid in the identification 
of the organisms in the test wells 102. The score form 150 thus enables 
the recording of test well valuations which enable both an identification 
of the organism and the minimum inhibitory count (MIC) as with form 120. 
Since a color comparison usually requires a different background color for 
analyzing the test wells 102, the shutter assembly lever 56 may, as 
appears necessary, be adjusted to a mixed background position relative to 
arm 30 as shown in FIG. 3. 
FIGS. 4 and 5 illustrate the alignment and construction features of the 
housing 22 and arm 30 with greater detail. These figures are section views 
of FIG. 2, but for purposes of clarity a mask 140 as shown and described 
with reference to FIG. 3 is shown in position. 
The arm 30 is in the form of a closed loop structure with its upper segment 
34 above the top surface 24 of housing 22 and the lower segment 36 below 
top surface 24 inside the housing. The arm moves on a centrally located 
shaft 160, which is attached to housing 22, with suitable linear bearings 
162 (only one being visible in FIG. 5). Nylon set screws such as 164 are 
used at the sides of lower segment 36 to slide on shoulders 168 of housing 
22 and maintain the arm 30 level. 
The lower segment 30 supports the test well illuminating and shutter 
assembly 50 below the test analysis section 26, the recording element 92 
below the test scoring section 28 and associated electronic drive circuits 
170 for the recording elements 92. 
Test well illumination is obtained with an elongate light source 172 formed 
in a U-shape and supported on a bracket 174 with spring elements 176. 
Light source 172 is a fluorescent light for which a conventional ballast 
(not shown) is also provided. The elongate light source 172 enables a 
uniform distribution of light along slot 52 in a shutter assembly 178 to 
illuminate each row 104 of test wells from the bottom. 
The light from light source 172 is passed through a light diffuser plate 
180 attached to the shutter assembly 178 and spaced therefrom with spacers 
182. The diffuser 180 provides a colored background, such as white. The 
light source 172 is so located to provide the desired light spectrum, such 
as an approximation of daylight. The shutter assembly 178 includes 
separate shutters 184, 186 attached to an aperture plate 188 as more 
particularly shown and described with reference to FIGS. 10-12. The 
aperture plate 188 has the test well illuminating slot 52 and is so 
positioned relative to reference edge 54 on arm 30 that a technician may 
view a row of test wells against either a light or dark background when 
looking vertically down along arrow 190. 
The up-turned edges 192, 194 (see FIG. 10) along slot 52 are formed in 
aperture plate 188 and reduce light from source 172 from reaching those 
test well rows 104 which are not in alignment with reference edge 54. 
Background illumination control is obtained by interposing one or both of 
the shutters 184, 186 in slot 52. 
In the view of FIG. 5, the shutter 186 is shown moved to a light 
interrupting position corresponding to the mixed position of the shutter 
lever 56 as shown in FIGS. 1 and 2. With this position of shutter 186, a 
dark background is presented to a technician looking straight down along 
the direction of arrow 190. Yet, the shutter 186 but partially blocks slot 
and leaves a narrow elongated aperture 191, not visible to the technician 
because of the shielding effect of the inclined edge 194. Light from lamp 
172 may pass through aperture 191 to illuminate the test wells, yet a dark 
background is provided for the visual analysis. The light angle through 
aperture 191 is selected to enhance readability of the wells. 
As illustrated in FIG. 4 and in greater detail in FIG. 6, the test scoring 
section 28 includes an array of electrically driven recording elements 
92.1-92.8 in the form of solenoids, each of which operates to drive a 
hammer plunger 193 through a slot 90 against a score form such as 120. In 
alignment with the travel path of a hammer plunger 193 is an anvil 94 
located on the other side of score form 120 and attached to the upper 
segment of arm 30. The top surfaces of the hammer plungers 193 are flat 
while the anvils are embossed with a symbol such as an arrow or other mark 
for pointing to a score value on the score form 120. The solenoid 
recording elements 92 are mounted to a bracket 195 attached to the lower 
segment 36 of arm 30 while electrically coupled with connectors to a 
circuit board (not shown) on which the drive circuits for the recording 
solenoids are located. The circuit board is also mounted to lower segment 
36 of arm 30 and includes suitable drive circuits as are well known to 
activate recording solenoids 92. 
FIG. 7 illustrates a detent mechanism 130 with which arm 30 is provided 
with discrete incremental index positions whereby reference edge 54 can be 
easily aligned with a row 104 of test wells 102. A rack 196 is shown 
connected to top surface wall 48 of housing 22 with suitable brackets 198. 
The rack 196 has a plurality of detents 200 along a lower edge 202. The 
rack 196 is so positioned that each detent 200 is in predetermined 
alignment with a row 104 of test wells 102 of a tray 100 placed in the 
test section 26. 
In contact with rack 196 is a roller 204 mounted on a spring element 206 
which biases the roller 204 to ride in and out of detents 200. Spring 
element 206 is mounted on a bracket 208 connected to lower segment 36 of 
arm 30. Hence, as arm 30 is moved along shaft 160, arm 30 has successive 
stable index positions to facilitate alignment of the arm 30 over the test 
analysis section 26. Suitable stops (not shown) are provided to limit 
movement of arm 30 along shaft 160 and prevent disconnection of roller 204 
from rack 192. 
With reference to FIGS. 8 and 9 and as previously mentioned, arm 30 carries 
score signal generators 70.1-70.8 which preferably are formed of membrane 
switches. These form a relatively flat profile on the top of arm segment 
34 yet with good tactile feel for the technician. The upper arm segment 34 
is shaped with a rigid metal bar 218 having a raised back edge 220, a flat 
surface 222 and a tapered front 224 leading to reference edge 54. 
A double adhesive layer 226 is placed on surface 222 and a conductor strip 
228 carrying a common conductor 230 and actuating conductors 231 is placed 
over layer 226. A thin spacer 232 with strips of double backed adhesive on 
both sides (but not shown) having a plurality of apertures 234 in 
alignment with switch positions 70.1-70.8 is then placed on top of strip 
228. A second conductor strip 234 carrying a plurality of separate 
conductors, aligned such as 236, is then located over spacer 232. A 
conductor such as 236 faces spacer 232 to make contact with the common 
conductor 230 through aperture 234 when depressed. A cover 238 carrying a 
strip of double backed adhesive material is placed over strip 234. Cover 
238 carries suitable printing legends 240 to denote the location of 
switches 70 as well as numerical characters as shown in FIG. 8. 
Electrical energization of switches 70.1-70.4 is obtained from suitable 
electrical circuit boards inside housing 22. Such energization may simply 
mean a connection of, for example, the common conductor 230 to ground or 
to some other potential while the other conductor 236 is connected in a 
circuit leading to activate a recording solenoid 92 or another recording 
device. The electrical connection of score signal generating switches 
70.1-70.8 is made in such manner that no wiring is visible from outside of 
housing 22. This is accomplished by leading the electrical conductor 
strips to a side end of the upper arm segment 34 and thence through an 
opening in the arm to the lower segment 36 for electrical connection to 
the recording solenoid drive circuits. 
Housing 22 includes a suitable conventional stationary power supply and 
a.c. source (not shown) to deliver power as it is needed for the test well 
illuminating lamp 172 and drive circuits for the recording solenoids 92. 
Electrical connection between the supply and the movable power requiring 
circuit elements on arm 30 is with flexible electric wires located to 
avoid excessive bending and interference with mechanical components. An 
on/off power switch 242 is located at top surface 24 as shown in FIGS. 
1-3. 
FIGS. 10-12 illustrate the shutter assembly without the light diffuser 
plate 180 as shown in FIG. 5. The shutters 184, 186 are in the form of 
plates and are mounted to aperture plate 188 for movement in the 
directions indicated by doubleheaded arrow 250. Sliding movement is 
controlled by pins 252 located through sets of slots 254, 256 in plates 
184 and 186 respectively. Plates 184, 186 are connected by a tension 
spring 258 which urges edge 260 of plate 184 to seat against bent-over lip 
262 of shutter plate 186. 
Hence, in one position of shutter control lever 56, as shown in FIGS. 4 and 
5 and in dotted outline at 264 in FIG. 11, the shutter plates 184, 186 are 
withdrawn and slot 52 is unobstructed. When the lever arm 56 is moved to 
the intermediate position as shown at 266 in FIG. 11, the action of spring 
258 causes both plates 184, 186 to move together. However, initially only 
shutter segment 268 of plate 186 is moved to partially obstruct slot 52 
and present a dark background for the test wells overlying the segment 268 
while still allowing light from lamp 172 to pass through a narrow aperture 
as previously explained. This condition coincides with the contact of pins 
252 with the ends of shorter slots 256 in plate 186. This type of mixed 
background illumination is normally suitable when both organism 
identification and minimum inhibitory counts are to be scored as described 
with reference to FIG. 3. 
When the lever 56 is further moved in the direction indicated by arrow 270 
in FIG. 12, the pins 252 prevent further movement of plate 186 but enable 
plate 184 to be moved until pins 252 engage the ends of slots 254 at which 
position segment 272 of shutter plate 184 completes obstruction of slot 
52. In both instances, the shutters 184, 186 do not completely close off 
slot 52 and thus permit light to come through, though shielded by inclined 
edge 194, at an angle onto the row of test wells in alignment with slot 
52. Hence, these wells can be observed against a black background with 
illumination still being applied. 
The housing 22 is formed of separate upper and lower castings which are 
suitably connected together. Similarly, the arm 30 and its upper and lower 
segments 34, 36 are formed of rigid castings to maintain structural 
integrity and alignments as described. 
Having thus described an apparatus in accordance with the invention for 
analyzing and evaluating tests in a plurality of wells in a tray, the 
advantages of the invention can be appreciated. The apparatus is formed to 
visually aid a technician and enable him in a semiautomatic manner to 
visually analyze the test wells and accurately evaluate his analysis in a 
rapid procedure. Variations from the described embodiment may be made by 
one skilled in the art without departing from the scope of the invention.