US 3660243 A
A petri dish compartment for a sterile ball for use with an automatic spreading element is provided with at least one sloping surface for release and recovery of the ball. The sloping surface has its highest point adjacent a recessed area in the compartment, the recessed area housing the spreading element prior to and after streaking.
Claims available in
Description (OCR text may contain errors)
United States Patent 1 1 Memes Young [4 1 y 2, 1972 PETRI DISH WITH COMPARTMENT R fer nces Cited FOR STERILIZED SPREADING UNITED STATES PATENTS ELEMENT 3,623,958 11/1971 Fitzgerald ..195/103.5
inventor: Cecil G. Young, La Canada, Calif.
Assignee: North American Rockwell Corporation Filed: Mar. 16, 1970 Appl. No.: 20,010
Primary Examiner-A. Louis Monacell Assistant Examiner-Robert M. Elliott Attorney-L. Lee Humphries, H. Fredrick Hamann and Robert G. Rogers  ABSTRACT A petri dish compartment for a sterile ball for use with an automatic spreading element is provided with at least one sloping surface for release and recovery of the ball. The sloping surface has its highest point adjacent a recessed area in the compartment, the recessed area housing the spreading element prior to and after streaking.
12 Claims, 7 Drawing Figures PATENTEDMM 2 1912 SHEET 10F 3 INVIZNTUR. CECIL G. YOUNG! ATTORNEY PATENTEDMM 21912 SHEET 2 UF 3 INVENTOR. CECIL G. YOUNG ATTORNEY PETRI DISH WITH COMPARTMENT FOR STERILIZED SPREADING ELEMENT REFERENCE TO RELATED APPLICATIONS "Automated Streaking Device for Isolating Micro-organisms on an Agar Surface," by James E. Fitzgerald, Ser. No.
BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an improved petri dish compartment for housing a sterilized spreading element for use in an agar culture automatic streaking device.
2. Description of the Prior Art One of the many procedures which must be performed in microbiology are plate streaks for isolating microbiological colonies. Distinctly isolated colonies are produced as a result of growth starting with a single cell. The isolated colonies are absolutely necessary for the observance of colony morphology and the performance of staining and other procedures necessary for determining the genus, and in many cases the species, strain, etc. of an unknown organism.
Examples of bacterialmicro-organisms which are isolated from samples include Staphylococcus aureus, Salmonella typhosa, Escherichia coli, and Neisseria ganorrhoeae. Examples of fungus type micro-organisms which are isolated from samples include Candida albicans, Actinamyces bovis, Cryptococcus neoformans, and Blastomyces dermatitidis. In an actual process, a liquid, for example isolation broths, blood, urine, etc. or solids, for example feces, scrapings, etc. might be used to identify an unknown bacteria. Fungi requires the same type of isolation as bacteria but, unlike the bacteria, the fungi are generally not subjected to additional tests since colony characteristics and microscopic appearance alone are usually adequate for their identification.
Generally, two or three plates are streaked per sample of the test specimen. The streaking process requires approximately 30 seconds per agar plate of a technologists time. The quantity of the streak and, therefore, the degrees of isolation of the micro-organism, depends on the training received by the technologist and the care taken in performing the process.
Problems typically encountered during a streaking process include the use of an improperly cooled inoculating needle following flame sterilization. As a result, the organisms may be destroyed during the streaking process. In addition, contaminants may be introduced by the use of an improperly sterilized inoculating needle. There are also the problems caused by the lack of reproducibility of streaks from one technician to another and the difficulty a technician often encounters in streaking soft agars which are easily cut. An improperly made streak must be redone before further testing is possible. The detection of a faulty streak may require anywhere from 12 to 48 hrs., depending on the rate of growth of the organisms present in the sample.
Several different manual methods are presently used by technicians to isolate micro-organisms from a specimen. Although any method is acceptable if it results in the isolation of the micro-organisms being streaked, it would be preferable if a device were developed for automatically streaking the micro-organisms.
An important step in the automatic streaking of an agar surface is the entry of the sterilized ball onto the agar surface. A similarly important event is the removal of the ball after streaking the agar surface. One of the problems in currently invisioned compartments for containing the sterilized ball is having a smoothly controlled entry of the sterilized ball to and from the agar surface. This particular problem is solved by the compartment of the present invention. The result achieved by the present invention is that the ball may be more gently placed on the agar surface and more positively controlled during entry to and from the agar surface. Of course. the sterilized condition of the ball prior to streaking and the complete isolation of the ball from the agar surface after streaking is still maintained.
However, a problem is encountered in placing the ball or an equivalent element at the proper location on the agar layer. The ball must be sterilized prior to use. Otherwise, micro-organisnts other than the micro-organisms of the specimen being analyzed may be spread on the layer. When the ball is sterilized outside of the petri dish, it is likely to be exposed to foreign bacteria, etc., in being positioned on the agar layer. Although the dish and ball can be sterilized together, the later deposition on the agar ordinarily covers the ball. Therefore, a petri dish is required which can contain the ball during sterilization without permitting the ball to be covered by agar, subsequently.
The present invention provides an improved compartment for use with a petri dish. The improved compartment allows for a positive control of the spreading element prior to streaking and complete isolation of the spreading element after streaking. Throughout the streaking operation and entry to and from the agar surface positive control of the ball can be achieved by an automatic or manual spreading element.
SUMMARY OF THE INVENTION The present invention comprises a petri dish having a cover and a compartment interior to the petri dish. The compartment has at least one sloping surface that extends toward the bottom of the petri dish from the compartment. The compartment is positionally spaced between the sloping surfaces if more than one sloping surface is utilized. The sloping surfaces have their highest points adjacent a recessed area in the compartment. A spreading element, usually a sterilized ball, is maintained in a recessed area of the compartment until needed for streaking of the agar surface. The ball is then removed from the recessed area and down one sloping surface onto the agar surface. After streaking of the agar surface the ball returns up the same slope or a second sloping surface of the compartment for return to the recessed area. The sloping surface therefore controls the ingress and egress of the ball to and from the compartment. In the preferred embodiment one sloping surface is used for placing the sterilized ball on the agar surface and a second sloping surface is used for retrieval of the ball from the agar surface.
Therefore, it is an object of this invention to provide a petri dish having an improved compartment with at least one sloping surface for controlling the ingress and egress of a sterilized spreading element.
It is a further object of this invention to provide a petri dish having a compartment for holding a sterilized ball and at least one ramp for improving the streaking process.
Another object of the present invention is to provide a petri dish having a compartment for containing a sterilized spreading element such that the control over the spreading element during entry onto and removal from the agar surface is improved when used with an automatic spreading element.
It is still a further object of this invention to provide a petri dish having a compartment for containing the sterilized ball wherein positive control by magnetic means for streaking the agar surface with the sterilized ball is achieved.
An additional object of the present invention is to provide-a petri dish having a compartment for holding a sterilized ball wherein the compartment has a recessed area with sloping surfaces down to the petri dish surface.
Yet another object of the present invention is to provide a petri dish having a compartment for holding a sterilized ball wherein the compartment has a recessed area that is divided into at least two distinct chambers.
These and other objects of this invention should become more apparent from the description of the invention, a brief description of the drawings of which follows:
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a compartment for a petri dish having the compartment along a portion of its circumference for enclosing a magnetic specimen sample-spreading element, such as a ball.
FIG. 2 is a perspective view of the compartment of FIG. 1 showing a variation on the sloping surface of the compartment.
FIG. 3 is a perspective view of a different embodiment of a FIG. 1 compartment for a petri dish wherein the slanted portion is oriented 90 from the FIG. 1 slanted portion.
FIG. 4 is a perspective view of a fourth embodiment of the compartment of the present invention having a recessed area flanked by two sloping portions.
FIG. 5 is a perspective view of another embodiment of the compartment of the present invention having a recessed area flanked by two sloping portions.
FIG. 6 is a perspective view of yet another embodiment of the compartment of the present invention having a recessed area flanked by two sloping portions.
FIG. 7 is a block diagram of a process for using a petri dish having a compartment such as described for one embodiment of the instant invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a perspective view of a compartment 10 located adjacent wall 18 an floor 19 of a petri dish 8. The compartment 10 has recessed area 12 for storage of a magnetic specimen sample-spreading element 1. Element 1 is shown as a steel ball which is a preferred embodiment. The recessed area 12 is depressed from the uppermost areas of the compartment 10. The interior walls of the recessed area 12 may be flat or they may slope to a low point for easy location of the magnetic element 1.
A vertical partition 13 separates the recessed area from radially sloping portion 14. The embodiment of FIG. 1 features one sloping portion leading to the floor 19 of the petri dish. A vertical partition 15 is at one end of the sloping surface 14. The cover of the petri dish has been omitted from the drawing to improve clearity.
In nonnal operation the magnetic ball 1 is at rest and maintained in the recessed area 12 of the petri dish with cover installed and an agar medium on the bottom of the petri dish. When the agar is to be streaked the magnetic ball 1 will be picked up by magnetic means operating through the cover of the petri dish. The magnetic ball then is lifted over the vertical partition 13 until it rests on sloping surface 14. The heighth that the ball must be raised to go over vertical portion 13 does not exceed the depth of the side of the lid of the petri dish such that exposure to any external contaminants is avoided during the transfer of the magnetic ball 1 from the recessed area to the agar surface. The magnetic ball 1 is then guided by the magnetic means down sloping surface 14 to the surface of the bottom of the petri dish. The magnetic means 1 might be transferred to a second magnet for positional control down the slope or a single magnet might serve as control for the magnetic means throughout transfer to the agar. Once the ball is at the bottom of the petri dish streaking of the agar surface can take place in a manner as shown by path 9. Magnetic control of the spreading ball may be assumed by another magnet after the ball reaches the surface of the agar. The streaking continues in a helical fashion with decreasing radii as the center of the petri dish is approached. Once streaking has reached the center of the petri dish the ball is retracted radially from the center of the petri dish back towards the sloping surface 14 as indicated by dotted path 11. The ball is returned up slop 14 over vertical section 13 and deposited back in the recessed area 12. The lid of the petri dish is not lifted far enough from the dish to allow any contaminates to enter the petri dish. Magnetic release of the ball is accomplished and the dish is then available for culturing.
A more detailed discussion of the process involved for streaking an agar surface in a petri dish having a compartment of the instant invention is associated with FIG. 7.
FIG. 2 is a perspective view of the compartment of FIG. 1 showing slight modification. The slight modification is the addition of vertical surface 17 extending from the surface of the bottom of the petri dish to a point that intersects slope 14 prior to slope 14 contacting the surface of the petri dish. Under certain streaking conditions increased control of the magnetic spreading element 1 can be realized by having such a vertical surface.
The perspective view shown by FIG. 3 is of a compartment wherein the sloping surface of the compartment is aligned circumferentially with the petri dish rather than radially as in FIG. 1. In FIG. 3 the compartment 20 is again adjacent the walls of petri dish 8 having vertical walls 18 and bottom surface 19. Magnetic spreading element 1 is located in recessed area 22. Recessed area 22 may have internally sloping surfaces to insure that the spreading element 1 is maintained at the center of the recessed area. Vertical walls 26 and 23 confine the spreading element to the recessed area. The walls of recessed area 22 in the circumferential direction of the petri dish further define the recessed area. In preparations for streaking the agar surface of a petri dish the spreading ball 1 is lifted by magnetic means over the vertical partition 23 and onto sloping surface 24. The sloping surface 24 may or may not have a heighth equal to vertical partition 23. In FIG. 3 the sloping surface 24 is shown to have a heighth somewhat less than the vertical surface 23 such that vertical surface 27 exists at the upper end of slope 24. Some benefit can be gained by having an arrangement as shown in FIG. 3 because the moving of the ball from recessed area 22 to sloping surface 24 can be accomplished with minimum raising of the petri dish cover. Also either one or two or any number of magnetic control means might be employed for handling the ball during the evolution for transfer from the recessed area onto the sloping surface.
The ball then is controlled down slope 24 onto the agar surface typical path being shown by the dotted lines 28. Once the ball is on the surface streaking of the agar surface will continue substantially as described for FIG. 1. Upon completion of the streak the ball will be returned in a radial manner to sloping surface 24 as shown by path 29. The sloping surface 24 might have a vertical region at the lower end much as described for sloping surface 14 in FIG. 2 and vertical surface 17.
FIG. 4 is a perspective view of a compartment 40 for maintaining the magnetic specimen sample-spreading element, wherein the compartment has two sloping portions. The magnetic ball 1 is maintained in recessed area 30. On two sides of recessed area 30 are sloping surfaces 32 and 35. In the embodiment of FIG. 4 sloping surface 32 has a slope oriented radially to the petri dish and leading to the surface of the bottom of the dish. Sloping surface 35 is oriented circumferentially to the petri dish. Vertical surfaces 31 and 36 confine the spreading element to the recessed area so long as the cover is on the petri dish.
Using the embodiment of FIG. 4 the magnetic ball 1 is picked up from the recessed area 30 and transferred over vertical surface 31 to the sloping surface 32. The ball is magnetically controlled down sloping surface 32 onto the surface of the agar that exists on the bottom of the petri dish. In the embodiment shown sloping surface 32 has vertical section 34 existing prior to the agar surface. Vertical surface 33 prevents movement of the ball off sloping surface 32 other than by controlled descent down sloping surface 32.
Once the ball is on the surface of the bottom of the petri dish, circular sweeps of decreasing radii collapsing towards the center of the petri dish commence, as shown by path 41. Once the streaking is done the ball may be radially moved to the outer rim of the dish to be controlled up ramp 35 as shown by path 42a and 42. The ball 1 is controlled up ramp 35. As the ball 1 approaches the top of slope 35 the lid on the petri dish is caused to slightly raise to allow the ball 1 to pass from slope 35 over vertical surface 36 and into recessed area 30. The petri dish cover is allowed to shut and the entrapped ball is magnetically released. The clearances between vertical sections 31 and 36 and the petri dish cover are such that the ball cannot escape from the recessed area 30 as long as the cover on the petri dish is maintained in tact and in place.
The ball 1 may be magnetically controlled radially inward to the center of the petri dish immediately after descending sloping surface 32. At the center of the dish the ball could be controlled through an increasing spiralling path from the center until a position approximate the outer circumference of the petri dish tracing a reverse of the path shown on FIG. 4. Ball 1 could then be controlled, as shown by path 42, up slope 35 to the recessed area 30.
FIG. 5 is an alternate embodiment of the compartment of FIG. 4 showing the sloping surfaces oriented 90 degrees from the embodiment of FIG. 4. In FIG. 5, ball I descends sloping surface 52 and is brought into contact with the agar layer in the petri dish. After ball 1 has completed the series of decreasing radial circular sweeps towards the center of the petri dish, as has previously been described, the ball is returned in a radial manner to a position approximate sloping surface 55. The ball is then controlled up slope surface 55, over vertical section 56, and into recessed area 50 where magnetic control of the ball is released.
The recessed area in all of the embodiments shown must have a depth sufficient to accomodate the specimen samplespreading device while pennitting the dish cover to fully close. Throughout the description the spreading element has been shown to be a metal ball, however, many other embodiments are possible such as a cylindrical pin, block or oblate spheroid.
In FIG. 6 there is shown a compartment 60 for use with a petri dish wherein said compartment has two recesses for maintaining the agar spreading element. The compartment has recessed areas 30 and 47 with sloping surfaces 32 and 35 on either side and adjacent to one of the recessed areas. The spreading element 1 is shown in its initial position in recess 30.
At one end of recessed area 30 is vertical surface 45 separating the recessed area 30 from sloping surface 32. Note that in this embodiment, the bottom of recessed area 30 raises to the top of vertical surface 45. Sloping surface 32 downwardly extends from alongside the recessed area 30 towards the bottom of the petri dish. A vertical surface 33 at one side of slope 32 assists the ball down the slope and does not permit motion of the ball off the slope. In the embodiment shown by FIG. 6 the sloping surface 32 ends at some distance above bottom surface 19 of the petri dish 8. It is of course within the discretion of the particular application whether or not to extend sloping surface 32 completely to the surface of the petri dish. On the other end of the compartment is sloping surface 35 extending from the bottom of the petri dish to recessed area 47. Slope 35 and recessed area 47 are separated by vertical surface 36 which drops from the highest level of slope 35 to the bottom of recessed area 47. Vertical partition 46 separates recessed areas 30 and 47 and insures complete isolation of the ball from the prior recessed area.
The bottom surfaces of the recessed areas 30 and 47 may be level or sloped as desired for the particular application. These surfaces may both slope towards the vertical partition 46 so that in either compartment the spreading element rests against partition 46. Similarly, each recessed area may have sloping surfaces towards their center or any other desired low point of the recessed area. It is of course desirable to have some low point in recessed areas 30 and 47 so that the spreading element will come to rest at a predictable location.
Dotted line 41 leading into dotted line 42a show a path that a spreading element would take under magnetic influence. It can be seen that the spreading element would exit from recessed area 30, travel downslope 32, streak the agar and return via slope 35.
It is a simple matter of design expediency to configure the compartments 30 and 47 with vertical surfaces 45 and 36 at either end so as to prevent the spreading element from leaving those compartments without raising the petri dish cover. In this manner complete isolation of the spreading element from the agar surface is maintained in all positions of the petri dish so long as the cover remains in place.
The compartments of the present invention may be constructed of any suitable material. Petri dishes are ordinarily comprised of transparent, plastic materials, however, other materials may be used as equivalents. For example, glass, wood, rubber or aluminum materials could be used. In one embodiment, the selected material must be capable of withstanding relatively high temperatures to which the dishes are subjected to sterilization. In other embodiments, the dish is sterilized by gas, such as ethylene oxide, at relatively lower temperatures.
The compartment may be manufactured as an integral part of the petri dish or manufactured separately and glued, bonded or otherwise attached to the petri dish.
Petri dishes may also be provided with covers that are suitable for contaminating the spreading element, such as a magnetic ball, while the spreading element remains in the compartment of the petri dish. Such a cover would avoid the need for transferring a contaminated spreading element into the petri dish compartment or raising the cover to spray, squirt or otherwise inoculate the spreading element with contaminate. An area of the petri dish covering is provided with a material such as rubber, styrofoam, sponge, fabrics such as nylon or cotton, paper, etc. through which a needle may be inserted. The needle penetrates the cover near the spreading element. Contaminate housed in the needle syringe is then injected onto the spreading element.
Alternately, the petri dish cover could be provided with the porous membrane such that the placing of contaminated material over the membrane causes contaminates to travel through the membrane to the spreading element. In this embodiment, complete integrity of the petri dish contents is maintained since penetration of the membrane by a needle is avoided and there is no need for raising the petri dish cover.
FIG. 6 is a block diagram of a process using a petri dish having a recessed area as described in the before discussed figures. Specifically, the description is directed towards the type of compartment shown in FIG. 6, although a similar description could follow for any of the compartments.
In the first step, 61, preferably a magnetic ball is placed in the compartment of the petri dish. The ball is specifically placed in the recessed area of the petri dish chamber, for instance with respect to FIG. 6 it would be chamber 30. If the ball is sterilized prior to being placed in the recessed area, care is taken to avoid handling the ball with anything but sterilized members. For example, a sterilized mechanical clamp could be used to move the ball from the sterilization cabinet onto the chamber.
If the ball has not been previously sterilized as is the usual case, it is sterilized in the chamber during the second step 62. In that case, the dish and the ball are sterilized simultaneously. During the sterilization, of course, the cover of the petri dish will remain in place.
In the third step, 63, the petri dish is filled with an agar layer to cover the bottom of the petri dish. The agar layer does not fill the petri dish but merely exists as a thin layer over the bot tom of the dish. The cover of the petri dish is replaced afterwards. Processes for filling the petri dish with agar are known to persons skilled in the art.
In the fourth step, the cover is removed and a specimen sample is placed in the compartment with the ball. In a last and preferred embodiment the specimen may be placed directly on the agar layer but, of course, the present invention is directed to schemes that avoid this.
Experimentation has indicated that by reducing the quantity of specimen placed with the ball, the amount of specimen spread on the agar layer is reduced at the beginning of the spreading operation. As a result, it is easier to isolate the micro-organism colonies produced during incubation period. In step five, 65, the petri dish 8 is placed on a rotatable table 68 as the table shown and described in the referenced patent application Ser. No. 808,914. A magnet 39 is positioned over the compartment 60 for attracting the ball 1. The magnet 39 may be automatically positioned by positioning motor 72 or it 1 can be done manually. With the recessed area of the compartment being sloping towards the low point center, the magnetic ball will always rest in a level petri dish at this low point in the center. This would allow simple positioning of the magnet 39 for picking up the ball.
When the magnet 39 is positioned over the ball 1 the ball is attracted toward the magnet. The force of the magnet pulling the ball forces the petri dish cover 73 upwards so that it may be lifted over the vertical partition 45 of recessed area 30. The magnet is moved by the positioning motor 72 and appropriate gears across the top of the cover until the ball is positioned down sloping surface 32 or at some other predetermined location relative to the agar layer 74 in the petri dish. Since the compartment has a sloping surface leading to the surface of the agar, the ball might in another embodiment be controlled by a magnet operating from the underside of the petri dish. The ball would be placed directly onto the surface of the agar after arriving at the bottom of sloping surface 32. In such a position, an additional magnet, such as 81, could take control of the ball and immediately commence the streaking of the agar surface in a manner as shown in FIG. 6. In another embodiment the ball could be transported directly to the center of the petri dish and then placed on the agar layer. The ball returns to the outer periphery of the petri dish under streaking action for retrieval via the sloping surface leading to the recessed area.
In step 66, magnet 81 is activated by positioning motor 76 to move in a straight line under the dish. Simultaneously, the table 68 is caused to rotate. As a result, the ball rolls along the agar surface in a non-overlapping pattern. More specifically, the ball and the dish rotate relative to each other so that the specimen sample is deposited on the agar in a spiral pattern. If the magnet 81 is positioned near the outer periphery of the petri dish the streak will spiral towards the center as the magnet is moved towards the center. If the magnet 81 is initially located at the center of the petri dish the streak will spiral towards the outer circumference of the dish as the magnet is moved away from the center of the dish.
As previously described in the referenced patent application Ser. No. 808,914 the specimen is deposited on the agar layer in decreasing amounts. By the time the ball is rotated to the center of the dish, (assuming that the ball starts from the outer periphery of the dish) isolated quantities are deposited. When the ball reaches the center of the dish, the magnet 81 is caused to rapidly move radially to the outer circumference of the dish. As the dish continues to rotate, clockwise as viewed from above in FIG. 6, the ball will be contacted by sloping surface 35. The magnet 81 is deactivated and magnet 39 is reactuated to place the ball into the recessed area 47. Of course it would be possible to exercise continuous control over the magnetic ball by a single magnet throughout the entire streaking evolution. A more complicated path would have to be traversed by the magnet, though, than is required by the scheme shown in FIG. 6. The magnet that lifts the ball from the recessed area and onto the sloping surface could lead the ball down the sloping surface and onto the surface of the agar. The magnet could then exercise control of the ball as it moved radially inward from the circumference of the petri dish towards the center. The petri dish table 68 would rotate as previously described. Once the ball is at the center of the petri dish then it could be lifted up and returned to the recessed area or could be returned in a single radial sweep to the sloping surface and rolled up the sloping surface. If the sweep progresses from the circumference of the petri dish towards the center, the region of decreasing micro-organisms would appear nearer the center of the petri dish as shown in step 7. As has been pointed out, the compartments of the present invention are particularly useful in this manner of streaking.
In step 7, numeral 67, the dish is placed in an incubator according to known techniques. After a required period of time, the micro-organisms grow on the agar layer as shown in the figure. The spiral pattern 78 is evident in the figure. The micro-organisms are taken from the dish for further study.
What is claimed is:
1. A petri dish, said dish comprising:
a floor portion holding an agar layer,
a magnetic ball element for spreading a specimen sample on said agar layer in said dish,
a compartment having a recessed area and at least one sloping surface extending from said recessed area to said floor portion; and
a removable cover for said dish common to said floor portion and said compartment.
2. The combination recited in claim 1 wherein said compartment comprises at least two sloping surfaces extending downwardly from said recessed area toward the bottom of said petri dish.
3. The combination recited in claim 2 wherein one of said sloping surfaces terminates prior to contact with the surface of the bottom of said petri dish.
4. The combination recited in claim 1 wherein said compartment has at least one sloping surface extending downwardly from said recessed area to the surface of said petri dish, the heighth of said sloping surface increasing along a circumference interior to said petri dish.
5. The combination recited in claim 1 wherein said compartment comprises at least one sloping surface extending downwardly from said recessed area to the surface of said petri dish, the heighth of said sloping surface increasing along a radius moving from the center of said petri dish towards the outer circumference of said petri dish.
6. The combination recited in claim 2 wherein said recessed area is located between two sloping surfaces of said compartment.
7. The combination recited in claim 6 wherein all surfaces of said recessed area are below the highest point of said sloping surfaces.
8. The combination recited in claim 4 wherein said compartment further comprises a vertical partition between said radially sloping surface and said recessed area.
9. The combination recited in claim 5 wherein said compartment further comprises a vertical partition between said circumferentially sloping surface and said recessed area.
10. The combination recited in claim 1 wherein said compartment has two recessed areas.
11. The combination recited in claim 10 wherein said two recessed areas are adjacent each other and wherein one sloping surface extends downwardly from each recessed area to the surface of the bottom of said petri dish.
12. A petri dish having sides including a cover having sides, said dish comprising:
a floor portion holding an agar layer,
a magnetic ball element to spread a specimen sample on said agar layer in said dish,
a separate compartment, said compartment having a recessed area, said recessed area having a partition therethrough,
a first sloping surface extending downwardly from a first partitioned area of said recessed area towards the surface of the bottom of said petri dish,
a first vertical separation between said first sloping surface and said first partitioned area of said recessed area, said vertical separation extending above the bottom of said recessed area and extending to a height above the bottom of said petri dish, the clearance between said cover and the uppermost part of said first vertical separation being insufficient to permit passage of said element to spread a specimen sample from said recessed area to said first sloping surface without necessitating the raising of said cover to permit passage of said element, said raising of said cover being to a heighth insuflicient to allow any portion of a side of said cover to be above any side of said petri dish,
a second sloping surface extending downwardly from a second partitioned area of said recessed area towards the surface of the bottom of said petri dish, and
a second vertical separation extending downwardly from the highest point on said second sloping surface to a second partitioned area of said recessed area, the
necessitating the raising of said cover to permit passage of said element, said raising of said cover being to a heighth insufficient to allow any portion of a side of said cover to be above any side of said petri dish.