Apparatus for culturing animal cells, method of culturing thereof and diagnostics of the culture

Abstract: This invention provides an apparatus for culturing animal cells, which comprises diagnosis means to make it possible to diagnose by measuring sizes of the cells by means of image processing while a system of culturing the animal cells is cut off from the outside of the apparatus system, control means to control the culture conditions of a culturing cistern on the basis of a result of the diagnosis, and culture medium re­ generating means to remove waste contents in a culture medium. In the apparatus of this invention, the culture system and diagnosis system are cut off from the outside of the apparatus system. Therefore, no infection of miscellaneous microorganism, etc., occurs, nor does consumption of valuable cells and products occur. Further, since it is possible to easily obtain data of the proportions of division potential-possessing cells and living cells, the environmental factors to the culturing cistern can be easily and instantly controlled based on the data, and therefore, the culturing efficiency can be enhanced.

Description: This invention relates to the culturing of animal cells, and particularly it relates to an apparatus for culturing animal cells which makes it possible to measure and diagnose the activity status of animal cells under culturing while maintaining the physiological conditions of the animal cells, a culturing method and diagnostics of the culture. The production of new medical drugs by the culturing of animal cells gives as small an output as some ng-µg/10⁶ cells·day. The improvement of the drug productivity requires (1) high densification of cells and formation of a high capacity apparatus and (2) achievement of high secretory activity of cells. In order to attain the above (2), it is necessary to measure activities of cells in a culture medium (survival, division, secretion, etc.) under the condition that the physiological conditions of the cells are maintained and the system is closed. However, under the present situation, it is general practice to determine proportions of living and dead cells according to a stain method in which a cell-staining agent is incorporated into a culture medium taken from a culturing vessel. In the above stain method, a staining agent is incorporated, etc., i.e., the measurement cannot be made under the condition that the physiological conditions of cells are maintained, and it is therefore not possible to return the culture medium to the culturing cistern. Accordingly, the measurement system is under the open system and it is impossible to prevent infection of miscellaneous microorganisms, etc. The rate of proliferation of animal cells is as small as 1/100 of that of microorganisms. Hence, the inclusion of one microorganism in the culture system means an end of new drug production activity. On the other hand, with regard to cells being cultured in a microscopically observable container such as a microplate, dish or culturing bottle, there is a proposal of a method by which to determine the status of cells, alive or dead, by image processing [Japanese Patent Kokai (laid-open) No. 201332/1987]. This method is applicable to species which is being cultured by using the above small containers. However, it is difficult to apply the above method to an apparatus of a practical culture scale. Further, the above method is merely to determine the "living or dead" status of cells, and there is no industrial method to determine the activity status thereof at present. DE 3139310 is concerned with morphological features used in determining the percentage of budding cells which serve in controlling the fermentation process. The document specifically deals with yeast or bacterial cells and not animal cells. It should be noted that yeast and bacteria have an extremely rapid rate of growth and are easily cultured. DE 3516529 discloses a turbidimetric measurement of microorganism culture such as cell, bacteriological, yeast and algae cultures, using a flow measuring cell. A cell size distribution is not at all measured. Moreover, the reference does not specifically disclose the measurement of animal cells. JP 62 201332 relates to a measurement of the number of cells by digitizing the cultured cell image taken into a device, processing the same by using a space filter and measuring the condition of the cultured cells. In the method of the reference, the numbers of live cells and dead cells are directly measured. Thus, the reference fails to teach a cell size distribution. JP 60 031888 discloses an automatic detection of the number of cases in the appearence of a fibrillar microorganism by analyzing the information of a microscopic image. EP 0 336 974, finally, relates to a cell propagation apparatus. According to the reference, culture cell is monitored by dyeing the cells. It is an object of this invention to provide a method for diagnosing the activity and culture status of cells sampled for the diagnosis, while maintaining the physiological conditions of the cells, and a method and apparatus for culturing cells which makes it possible to diagnose activity status of the cells without exerting any harmful influence on the culture system, and an apparatus for working the above method. According to the present invention this object is solved by the methods described in claims 1 and 2, respectively, and by the apparatus described in claim 4. This invention can be applied to culturing animal cell strains such as human lymphoblast (IM-9: U.S. A.T.C.C.), rat liver cell JTC-1, mouse-mouse hybridoma (STK-1: U.S. A.T.C.C.), etc. Needless to say that this invention is applicable to culturing of any cells that exhibit a cell size distribution as shown in Figure 1 which will be discussed later. Figure 1 shows experimental data for sizes and distribution states of animal cells. Figure 2 shows a model for states of growth, division and death of animal cells. Figures 3 to 5 are schematic views showing a device for diagnosing cell activity in this invention. Figures 6 and 7 are schematic views showing the diagnosis of cell activity and control system of culturing cistern in this invention. Figures 8 to 9 show typical views for a method of processing images of cells which are being cultured. Figure 10 shows an example of the resultant cell diameter distribution. Figure 11 shows an apparatus for diagnosing cell activity as one embodiment of this invention. Figure 12 shows a device for controlling diagnosis of cell activity as one embodiment of this invention. Figures 13 and 14 schematically show perspective views of a cell for diagnosing cells as one embodiment of this invention. According to Figure 1, the judgement on the "living or dead" state of cells will be explained. Figure 1 shows one example of cell size distributions obtained by microscopic observation of about 100 cells fixed by the stain method from rat liver cells JTC-1 in a steady state during a culturing process. In the Figure, that portion of the distribution which is indicated by hatching shows living cells, and that portion of the distribution which is indicated by void shows dead cells. The sizes of cells are distributed in the range from 10 µm and some to 40 µm and some. And the living cells are distributed on the smaller-number side and dead cells are distributed on the larger-number side. The above distribution consists of 1 ○ a region of only living cells, 2 ○ a region of both living and dead cells, and 3 ○ a region of only dead cells. On the basis of the above characteristic constitution of distribution, it is possible to determine proportions of living cells, dead cells and division potential-possessing cells. The living cells/dead cells ratio in the above region of both living and dead cells is 1:1, and the living cells in the region of both living and dead cells do not have any division potential. The living cells distributed in the above region 1 ○ have division potential. The above distribution of cell sizes is in agreement with progressive phenomena of growth, division and death of cells typically shown in Figure 2. Statistically, when a cell grows to a certain size (two-dimensional size: its area is taken as 1), the cell undergoes division, and physically, its area after the division is 0.64 of the area which the cell had before the division. When reproduced cells grow to a size having an area of 1, the cells undergo division. The areas of division potential-possessing cells range between 0.64 and 1. A cell, which does not undergo division any longer, further grows over the area of 1 until its final death. After a cell dies, cytoplasms such as mitochondoria, etc., flow out of the cell, and the cell swells to increase its size apparently. Its nucleus disappears and finally the cell is dispersed in a culture medium. In correspondence between the course of growth, division and death and the distribution of cell sizes shown in Figure 1, the state of area of 1 corresponds to a boundary between the distributions 1 ○ and 2 ○ , and the state of final death of the cell corresponds to a boundary between the distributions 2 ○ and 3 ○. An actual course of cell culturing shows variations in the sizes of cells which finally die, and therefore the distribution 2 ○ appears. In the living cells/dead cells ratio in the distribution 2 ○ , the smaller the cell sizes are, the larger the proportion of living cells is, and the larger the cell sizes are, the smaller the proportion of living cells is. The living cells/dead cells ratio in the distribution 2 ○ is nearly 1:1. As mentioned above, it is possible to determine the living/dead ratio and division activities of cells by measuring cell size distributions. The measurement of cell size distributions can be carried out without incorporating any foregign substance into a culture system. Therefore, the above activities of cells can be diagnosed without isolating the cells from their culture system. EXAMPLES Figure 3 shows a device for diagnosing cells as one embodiment of this invention. The apparatus comprises a culturing vessel 1, a culture medium observing portion 2, means 3 of introducing a culture medium to the observing portion 2, a measuring device 4 to measure sizes of cells in the observing portion 2, an analyzer 8 to determine a proportion of division potential-possessing cells (or proportion of division potential-not possessing cells) or a proportion of living cells (or proportion of dead cells) on the basis of a cell size distribution, and means 6 to return a culture medium in the observing portion 2 to a culture medium in the culturing cistern. The means 3 and 6 and the observing portion 2 are constituted such that the culture medium can be recycled under a condition of its isolation from the outside the culture system. The culture medium in the culturing vessel is partially fed to the observing portion 2, and cells in the partially fed culture medium in the observing portion 2 are measured by the measuring device 4 for a cell size distribution. An equivalent diameter or area may be used to represent the cell size. When the measurement is finished, the culture medium in the observing portion 2 is returned into the culturing vessel 1. An information on the cell size is transmitted from the measuring device 4 to the analyzer 8, and the analyzer 8 determines activity of cells (division activity, life-maintenance activity) on the basis of the above information to display the result. In general, the culture medium is intermittently fed from the culturing vessel 1 to the measuring portion 2. However, there are some types of measuring devices which can measure the above distribution while the culture medium is fed continuously. Figure 4 shows a device for diagnosing cell activity as one embodiment of this invention, in which an image processing device is used in the above measuring device 4. The image processing device comprises an image taking means 4′ and an image processing means 5. An image of cells is transmitted from the image taking means 4′ to the image processing means 5. Preferably, the image taking means 4′ has a magnifying function such as a microscopic function. The flow rate of a culture medium in the observing portion 2 may be about a rate of precipitation of cells in a stationary culture medium. Figure 5 shows detailed constitutions of the image processing device 5 and the analyzer 8, and their actions will be explained hereinbelow. At first, image signals obtained by the image taking device 4′ are transmitted to an A/D converter 51 of the image processing device 5. The A/D converter 51 converts analog signals of an image to digital signals. That is, the image is not only divided vertically and horizontally into small pixels, but also A/D converted image signals are formed into a multi-element image in which the pixels have digital brightness values. For example, an image is divided vertically and horizontally into 256 by 256 pixels and digitized with resolution of 128-step brightnesses. The A/D converted image signals are stored in an image memory 51M. The multi-element image stored in the image memory 51M is transmitted to a cell image recognition circuit 60. The cell image recognition circuit 60 recognizes all of the cells regardless of their life or death, calculates their number and sizes, and calculates their particle diameter distribution. The calculation results are transmitted to the analyzer 8, and the analyzer calculates, on the basis of the above calculation results, the numbers of living cells and dead cells and the number of division potential-possessing cells, and at the same time diagnoses activity status of the grouped cells on the basis of these calculation results. Figure 6 shows an embodiment of multi-value image data stored in the image memory 51M. The multi-element image stands for an image of which the pixels are different in the brightness, as explained previously. Some cells have large sizes and the other cells have small sizes. In Figure 6, cells having small particle diameters represent living cells, and cells having large particle diameters represent dead cells. Cells having diameters in between represent those in the state in which living cells and dead ones are co-present. The image in Figure 6 is transmitted to the cell image recognition circuit 60, which recognizes all of the cells regardless of their life or death, and calculates the number, size, form and brightness of the cells, etc. This Example will explain a calculation of the size and number. A pre-processing circuit 61 effects the pre-processing in order to recognize the cells from the multi-element image of the image memory 51M. Examples of the preprocessing include smoothing, brightness emphasis, outline emphasis, etc. However, in order to recognize cells, mere spatial filtering treatment is not sufficient in accuracy, and particularly, brightness emphasizing treatment before the spatial filtering treatment is effective. The maximum brightness emphasizing treatment is one type of nonlinear neibourhood calculation, and its specific details will be explained according to Figure 7. In a region of 3 x 3 pixels (of which the brightnesses are indicated by k₁ to k₉) having a pixels of brightness k₅ in the middle as shown in Figure 7, the maximum brightness in the region is newly substituted in the picture element of brightness k₅. The calculation formula is as follows. k₅ = MAX [k₁ ∼ k₉] (1) For example, if k₁ is the highest brightness among k₁ to k₉, i.e., MAX [k₁ ∼ k₉] = k₁ , then the brightness of the pixel having a brightness k₅ is changed to k₁. All the picture elements are treated in the same way as mentioned here to obtain a new multi-value image data. This treatment has a function to emphasize the brightness of the central portion of a cell since the central portion has high brightness. Further, there is also a function to erase dark portions of a cell outline. In addition, in the pre-processing circuit 61, it is further effective to carry out spatial filtering treatment in order to emphasize bright portions by using a mask pattern shown in Figure 8. In Figure 8, p's represent positive values, and m's represent negative values. This treatment makes it possible to selectively emphasize cells alone. A binalization circuit 62 achieves binalization in which portions having higher brightnesses than the given brightness k a are set as "1" and the other portions as "0". Figure 9 shows an image obtained by this binalization of the image of Figure 6. In Figure 9, portions indicated by slanting lines show background, and void portions show cells. If cells are large and interiors of the cells are binalized as blank, blank-filling treatment is carried out, although its explanation is omitted here. By the above procedures, it is possible to selectively recognize cells alone. The parameters, m, p, k a , etc., which are necessary for the preprocessing and binalization, are set by a conditioning circuit 66. With regard to an image binalized by the binalization circuit 62, a labeling circuit 63 labels numbers on cells therein and counts their numbers, and every cell is subjected to the following treatment. That is, a next area calculation circuit 64 calculates an area of every cell. Then, a circuit 5, for calculation of a cell diameter distribution, calculates a diameter by classifying areas of the cells. For example, the classification is effected every 1 µm. In this case, a circle-equivalent diameter, etc., may be used as a typical cell diameter. The calculated cell diameter distribution is transmitted to the analyzer 8. The analyzer 8 receives values of the cell size distribution and diagnoses activities of the cell groups totally. An example of the resultant cell diameter distribution is shown in Figure 10. This principle is accomplished by forming a model of a relationship between growth of cells (increase in cell diameter) and their diameter distribution. That is, in the analyzer 8, a living cell calculation circuit 81A, a dead cell calculation circuit 81B and a co-present cell calculation circuit 81C calculate numbers of grouped cells, respectively. In other words, a formula of living cells (2), formula of dead cells (3) and formula of living and dead cells co-present state (4) are formed into models with separate distributions of each diameters. Namely, provided that cell diameters present in boundaries of the grouped cells are d am and d me as shown in Figure 10: living cell d ≦ d am : N(d a ) = F a (d) (2) dead cell d > d me : N(d e ) = F e (d) (3) co-presence d am < d ≦ d me : N(d m ) = F m (d) (4) total number of cells : N t (d) = N(d a ) + N(d e ) + N(d m ) (5) In the above formulae, d a , d e and d m represent cell diameters of living cells only, dead cells only and living and dead cells co-present state, respectively, and N(d a ), N(d e ) and N(d m ) represent numbers of such cells, respectively. Further, F a (d), F e (d) and F m (d) are functions of cell diameter distributions, and F a (d) is a normal distribution, F m (d) is a homogeneous distribution and F e (d) is a monotone decrease type distribution (e.g., exponential distribution). As mentioned here, the living cell calculation circuit 81A, dead cell calculation circuit 81B and co-present cell calculation circuit 81C carry out calculations to apply models-forming particle diameter distributions to the cell particle diameter distribution transmitted from the cell image recognition circuit 60, thereby to determine the cell diameters d am and d me which are boundaries of the individual distributions. If the boundary cell diameters d am and d me are determined, N(d a ), N(d e ) and N(d m ) can be easily obtained from the cell diameter distribution transmitted from the cell image recognition circuit 60. The above N(d a ), N(d e ) and N(d m ) can also be obtained by inputting d am and d me through the conditioning circuit 82 in the steady state. The number of cells in each of the distributions can be calculated as mentioned above. Therefore, various activities of the cell groups as a whole can be diagnosed. Diagnostics will be discussed concretely hereinbelow. An activity calculation circuit 83 calculates, for example, a cell survival rate ε in the following formula. In the activity calculation circuit 83, a division portential-possessing cell ratio η is calculated in the following formula. Similarly, in the activity calculation circuit 83, a dead cell ratio R e is calculated in the following formula. In addition to the above, in the activity calculation circuit 83, temporal changes of living cells { N(d a ) + 1/2N(d m ) } and dead cells { N(d e ) + 1/2N(d m ) } are calculated, i.e., a rate of proliferation and a rate of death are calculated in the following formulae. On the basis of these formulae, cells are diagnosed for proliferation, activity decrease or death state. For example, even if R e is large, the higher rate of proliferation indicates the higher proliferation potency and activity of the cells. Even if R e is small, the higher rate of death indicates not only rapid death of the cells but also low activity of the cells. The activities of cell groups are diagnosed as mentioned above. These diagnostic results are inputted to an inference engine 95. Also inputted to the inference engine 95 are values measured by a temperature sensor, a pH sensor, dissolved oxygen (DO) sensor and a dissolved carbon dioxide gas (DCO₂) sensor as cell culture environmental factors. On the other hand, assorted experimental and theoretical data of proliferation and metabolism of cells are stored in a data base 90. The inference engine 95 infers status of cells on the basis of information of the data base, measured values of culture environment and diagnostic results of image-measurement of cell groups, and inputs a command to a computer as necessary in order to control the culture environment. For example, when DO decreases to lower the proliferation rate of cells, the inference engine 95 infers DO shortage and increases the rate of bubble generation by a compressor to increase DO. When pH lowers to increase the rate of death, the inference engine 95 infers that pH is too low, and increases pH by feeding an alkali agent, adjusting the partial pressure of carbon dioxide gas, or the like. Figure 11 shows an apparatus for diagnosing cell activity as one embodiment of this invention. This apparatus is an integral constitution of the culturing vessel 1 and observing portion 2 shown in Figure 4, in which a culture medium in the culturing vessel is partially fed to the observing portion 2 by a spinner flow in the culturing vessel and the culture medium is returned from the observing portion 2 into the culturing cistern. Figure 12 shows a device for controlling diagnosis of cell activity as one embodiment of this invention. This apparatus comprises a culturing vessel 1 having means (1′, 1″, 1‴, etc.) of adjusting environmental factors to a culture medium within the culturing cistern (nutrition contents concentration, dissolved oxygen concentration, concentration of waste products such as ammonia, lactic acid or the like, ages of cells, product concentration, etc.), an observing portion 2, an introduction device 3 to introduce a culture medium to the observing portion 2, a measuring device 4 to measure a distribution of cell sizes in the observing portion 2, an analyzer 8 to determine, from the cell size distribution, a proportion of division potential-possessing cells (or proportion of division potential-not possessing cells) or a proportion of living cells (or proportion of dead cells), and means 6 of returning the culture medium in the observing portion 2 into the culture medium within the culturing cistern. The above means 3 and 6 and the observing portion 2 are constituted such that the culture medium is recycled under the condition that it is cut off from the outside the culture system. The culture medium in the culturing cistern is partially fed to the observing portion 2, and cells in the fed culture medium are measured by the measuring device 4 for a distribution of their sizes. Nominal diameters, areas, etc., may be used to represent sizes of the cells. The culture medium used for measurement in the observing portion 2 is returned into the culturing vessel 1. An information of a cell size distribution is transmitted from the measuring device 4 to the analyzer 8, which determines cell activities (division activity, survival activity) on the basis of the above information. Further, the analyzer 8 properly adjusts the environmental conditions to the culture medium in the culturing vessel by controlling the above adjusting means 1′, 1″, 1‴, etc., on the basis of the resultant cell activities. The method of controlling the environmental conditions to the culture medium in the culturing cistern will be explained hereinbelow. By using a proportion η of division potential-possessing cells (= number of division potential-possessing cells/number of living cells) and a proportion ε of living cells (= number of living cells/number of total cells), the number N of living cells to be found in t hours' time can be represented by the following formula. wherein if (n + 1)T > t ≧ nT, then t / T = n In the above formula, N₀ represents a total cell number when t=0 and T is a cell cycle, and n is 0 or a positive integer. That is, it is possible to simulate the number of living cells in t hours' time by using formula (11). On the basis of the result of the above simulation, it is also possible to control the environmental conditions to the culture medium in the culturing vessel. In addition to the dissolved oxygen concentration, nutrition contents concentration and waste contents concentration in the culture medium, the above environmental conditions include the following values P and Q. P = cell concentration x stay time (12) By controlling the above value P or Q such that it is in a given range while considering the above environmental conditions, it is possible to control various activities of cells (respiratory activity, proliferation activity, secretory activity, endogenous respiratory activity, etc.). That is, it is possible to control activities optionally; for example, the proliferation activity can be enhanced more than the other activities, the secretory activity can be enhanced more than the other activities, and the like. The following is an explanation of a measuring device cell to measure the cell sizes in this invention. Figure 13 is a perspective view showing one embodiment of said cell. Figure 14 is a typical perspective view of a cell portion in which a culture medium of cells flows. The observing portion cell 2 has a cell structure as shown in Figure 14, which is formed by using, as a spacer 11, a film of polytetraethylene (having a thickness of about 100 µm) with a hexagonal window, and placing the film between two glass sheets 12 and 13. The two glass sheets are fastened by two metal supporter frames 16 and 17 and screws (not shown). The cell is provided with an inflow tube 14 of a cell culture medium and an outflow tube 15 thereof. In addition, the observing portion cell can be subjected to sterilization treatment under heat (120°C). Further, the above cell is placed on a stage 18 which is movable freely in the direction of X-Y, and is provided with a constitution which makes it possible to make observation through the measuring device 4 placed above the cell and by light emitted from a light source (not shown) placed in the lower portion of the stage. A culture medium is introduced into the cell by the inflow tube 14 from a circulation pipe (not shown) connected to the culturing cistern, and the stage and an observing device are manipulated to observe sizes of animal cells. In diagnosis of the activity status of cells, an image of cells, which is taken by a image making device (indicated as 4' in Figure 4) attached to the measuring device 4, is processed by an image processing means (indicated as 5 in Figure 4), and the resultant data is diagnosed by an analyzing means (indicated as 8 in Figure 4). The culture medium containing the measured cells is returned to the culturing cistern through the outflow tube 15. As mentioned above, since this embodiment makes it possible to diagnose the activity status of cells in the state where the culture system and diagnosis system are cut off from the outside the apparatus system, there is not any risk of miscellaneous microorganisms infection, nor is there any loss of products such as a culture medium, etc. As discussed hereinabove, in this invention, the culture system and diagnosis system are cut off from the outside the apparatus system. Therefore, there is no infection of miscellaneous microorganisms, etc., and valuable cells and products are not consumed. Further, since it is possible to easily obtain data of the proportion of division potential-possessing cells and the proportion of living cells, it is easily and instantly control the environmental factors to the culturing cistern on the basis of the data. Therefore, the culturing efficiency can be enhanced.

Claims: A method of diagnosing activity status of the animal cells during culturing the cells, which comprises the steps of: taking part of a culture liquid containing the animal cells out of a culturing vessel (1); taking an optical image of the part of the culture liquid through an optical device; converting the optical image into electrical signals; measuring sizes of animal cells in the part of the culture liquid on the basis of the signals by image processing; calculating a cell size distribution of the animal cells, to obtain cell diameters present in boundaries of grouped cells in the distribution; and diagnosing activity status of the animal cells from thus obtained boundary cell diameters, wherein the same physiological conditions of the taken part of the culture liquid as in the culturing vessel are maintained while the taken part of the culture liquid is out of the culturing vessel. A method of culturing animal cells, which comprises the steps of: taking part of a culture liquid containing the animal cells out of a culturing vessel (1) which is isolated from the atmosphere; taking an optical image of the part of the culture liquid through an optical device; converting the optical image into electrical signals; measuring sizes of animal cells in the culture liquid by image processing on the basis of the electric signals; calculating a cell size distribution of the animal cells on the basis of the cell sizes, to obtain cell diameters present in boundaries of grouped cells in the distribution; diagnosing activity status of the animal cells from thus obtained boundary cell diameters; and returning the taken part of the liquid to the culturing vessel (1), wherein the taken part of the culture liquid is isolated from the atmosphere and the same physiological conditions of the taken part of the culture liquid as in the culturing vessel is maintained while the taken part of the culture liquid is out of the culturing vessel (1). The method according to claim 2, wherein the cell size distribution is divided into three portions, first one of which is normal distribution as a living cell region, second one is a homogeneous distribution as a co-presence of living cell and dead cell region, and third one is a dead cell region. An apparatus for culturing animal cells, which comprises: a culturing vessel (1) for containing a culture liquid containing animal cells and for performing culturing of animal cells therein; means for feeding a fresh culture medium to the culture liquid in the culturing vessel (1); means (3, 6) for taking from the culturing vessel (1) a part of a culture liquid containing the animal cells and for returning the part of culture liquid to the culturing vessel; means (4, 5) for picking up an optical image of the animal cells in the part of culture liquid taken outside of the culturing vessel and for converting the optical image to electrical signals; means (8) for processing the electrical signals to obtain cell size distribution and then to obtain the cell diameters present in boundaries of grouped cells in the distribution; and means for outputting processed information including thus obtained boundary cell diameters, wherein control means (95) are provided so that the physiological conditions of the culture liquid outside of the culture vessel are maintained in the same as in the culture liquid in the culture vessel until the culture liquid is returned to the culture vessel. The apparatus according to claim 4, wherein the culture liquid is isolated from the atmosphere during the whole period of culturing.

Inventors: BABA KENJI, HAGA RYOICHI, ISHIDA MASAHIKO, MARUHASHI FUMIO, MATSUZAKI HARUMI, NISHIMURA NOBUKO, NISHIMURA YUUSAKU, SAITOH SETUO, BABA, KENJI, HAGA, RYOICHI, ISHIDA, MASAHIKO, MARUHASHI, FUMIO, MATSUZAKI, HARUMI, NISHIMURA, NOBUKO, NISHIMURA, YUUSAKU, SAITOH, SETUO
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1989
Main classification: C12M3
IPC codes: C12M1, C12M3, C12N5, G01N33, C12N1