referring now to fig1 the schematic representation of the sterilization apparatus includes a cylindrical housing 1 , that is surrounded by a jacket 2 spaced therefrom , defining an interspace for a heating or cooling auxiliary fluid . within the housing there is removably disposed a rack 3 , having a plurality of open shelves 4 through which an operating fluid can flow , and which supports containers 5 filled with a substance to be sterilized . at the top portion of the housing 1 is located a whirl fan 6 driven by an electromotor 9 via a shaft 7 , and a belt drive 8 . cooling devices 11 are arranged between the housing 1 and the rack 3 ; the cooling device 11 is from time - to - time filled with a cooling medium , which medium is again discharged from time - to - time from the cooling device 11 . inlets 1a serve for introducing a hot steam - air mixture into the inner space of the apparatus housing 1 , after the rack 3 with the containers 5 has been inserted , and the housing has been closed by a door or cover , for example . an outlet 1b is employed for discharging the condensates . in known sterilization devices of the above - described type the operating medium is whirled around by means of a fan 6 in the sense of the arrows p 1 or p 2 , in such a manner that the operating medium flows , for example , from below the rack 3 to there above substantially uniformly . due to the fact that a hot operating medium transfers heat to the containers 5 during the heating - up period , and therefore is first cooled down , while streaming through the rack , and also due to the fact that the operating medium cooled down by the device removes heat from the containers during the cooling period , and consequently is warmed up by the flow of the medium through the rack , the containers arranged in the lowermost shelf 4a , in the middle shelf 4b , or in the uppermost shelf 4c are heated up , each at a different rate , and upon sterilization are again cooled at different speeds , as shown in the temperature vs . time diagrams t a , t b , and t c of fig2 a . the sterilization cycle lasts the entire charging time t c and includes the heating - up time t h , the sterilization time t s and cooling - down time t k . as the sterilization time t s can be counted only from the moment t h , at which moment containers located at the uppermost shelf 4c have reached the sterilization temperature t s , the individual containers during the entire charging time t c are subjected to the sterilization temperature for different time intervals , and consequently a non - uniform treatment will result , and in certain cases the containers may become damaged due to excessive exposure of the containers to the sterilization temperature . this drawback is avoided in the embodiment of the present invention , according to fig1 by connecting the electromotor 9 via a phase switch 15 to a three phase alternating current network , and by controlling the phase switch 15 by the timing - and controlling - device 16 in such a manner that the rotational direction of the electromotor is periodically reversed for time intervals that are short relative to the heating - up period t h , or the cooling - down period t k . as a consequence the whirling movement of the operating medium through the rack 4 alternates in the direction of arrows p 1 and p 2 , as indicated in fig1 . in this way the characteristic curves of the temperature during the heating - up time and the cooling - down time follow a single average value t &# 39 ; as indicated in fig2 b , so that the heating - up time and the cooling - down time , and therefore the whole charging time t c are substantially reduced , in spite of the fact that the sterilization time remains the same ; the reduced time periods are indicated in fig2 b by t &# 39 ; h , t &# 39 ; k or t &# 39 ; c . instead of reversing the direction of the whirling stream of the operating medium by reversing the rotation of the driving motor for the fan , as explained above , with reference to fig1 the timing and controlling device 16 may also control the angular adjustment of the blades of the fan 6 in a sense so as to cyclically reverse the effective operative direction of the fan . another reduction of the heating - up and cooling - down times , and of the charging time to values t &# 34 ; h , t &# 34 ; k , or t &# 34 ; c in fig2 c is attained in the embodiment of fig1 by introducing , through the inlet 2a , saturated steam into the interspace between the jacket 2 and the housing 1 , prior to the insertion into the housing 1 of the rack 3 containing articles to be sterilized . upon placement of the rack 3 into the housing 1 , it is nessary to heat up only the substance to be sterilized by the steam - air mixture introduced through the inlets 1a . the precipitated condensate is discharged from the outlet 2b . in a similar manner the cooling of the substance to be sterilized can be achieved more quickly by introducing cooling water through the inlet 2c into the interspace between the jacket 2 and the housing 1 , following the expiration of the sterilization time t s , so that the outlet 2b is first closed , but upon expiration of the cooling time is again opened to discharge the cooling water . by this means , as seen in fig2 c on characteristic curves t &# 34 ;, a faster heating - up or cooling - down time will result , so that in comparison with the state of the art shown in the diapram of fig2 a , the total sterilization time and the charging time is reduced two - fold due to the reduction of both the heating - up , and the cooling - down intervals . in a sterilization process having a sterilization temperature of 120 degrees centigrade and a sterilization time t s of 30 minutes , the heating - up time , the cooling - down time , and the charging time can be reduced , in comparison with the process according to fig2 a , by applying the process of the present invention ( fig2 b or fig2 c ) as follows : another embodiment of this invention is illustrated in fig3 a and 3b , where like components are denoted by the same reference numerals . in contrast to the embodiment of fig1 the fan 6 in the apparatus of fig3 a always operates in the same effective direction , and the cooling device 11 is arranged in a radially extending stream path from the fan 6 . whereas in the example of fig1 there is provided a stable path of the steam of the operating medium , in the example of fig3 a there are created three partial streams on each side of the sterilization chamber , namely partial streams indicated by arrows p 1x , p 2x , p 3x , and p 1y , p 2y , p 3y . the operating medium is divided into the partial streams by means of switching or shifting control members that in the given example are in the form of valves or lids 20 1x , 20 2x , 20 3x , and 20 1y , 20 2y , 20 3y . this arrangement makes it possible , for instance , by opening two selected valves , to produce substantially symmetrical , and axial partial streams of the operating medium . by opening another selected pair of the valves , the partial streams can be directed transversely and / or in opposite directions through the rack 3 . an axial stream corresponding to arrows p 1x and p 1y occurs on opening the valves 20 1x and 20 1y , a transverse or oblique stream , corresponding to arrows p 2x and p 3y takes place after opening valves 20 2x and 20 3y , and another oblique stream corresponding to arrows p 3x and p 2y results by opening the valves 20 3x and 20 2y . as disclosed in fig3 b , the alternate opening of valves can be controlled by the timing and controlling device 16 , that transmits a succession of electrical pulses to pneumatic valves 21 , 22 and 23 , which allow a pressure air source 24 to alternately transmit compressed air to a pair of pneumatic cylinders 25 ; the pistons of the cylinders are linked to an assigned pair of valves as indicated only schematically in fig3 a . the valves in the housing 1 , such as for example , valves 20 1x and 20 1y , are spring - biased towards the closing position , and by the application of the controlling pulses the pistons act against the tension springs and open the valves 20 during operation of the controlling device 16 . in the embodiment according to fig4 the apparatus housing 1 has a prismatic configuration , and is provided with a system of valves or lids 20 operating in a similar manner as those in fig3 a . the paths of partial streams are also indicated by arrows p 1x , p 2x , p 3x , p 1y , p 2y , and p 3y . contrary to the embodiment of fig3 a , the valves 20 in fig4 are not cyclically and alternately opened and closed , but are adjusted by means of valves and servomotors 35 in response to processed signals from temperature sensors 31 , 32 and 33 arranged in different places in the rack 3 . the signals from the sensors are first applied to a computer or a data processor 34 , that processes the received signals , and in turn commands the valves and servomotors 35 , so as to achieve a uniform average temperature of the operating medium in the whole region of the sterilization chamber . to this end the computer 34 compares the different temperature readings with one another , and delivers an output control signal to the servomotors 35 , which motors are coupled to the valves 20 1x , 20 2x , 20 3x , 20 1y , 20 2y and 20 3y and adjust the same either individually or in groups , so that the region having the lowest temperature during the heating - up period is heated by a more powerful partial stream of the heating medium , or in cooling down the region having the highest temperature , is cooled by a more powerful stream of the cooling medium . the data processor for this purpose can be of any suitable well known conventional type in the art , and need not therefore be explained in detail . while this invention has been explained and illustrated as embodied in a specific examples of a sterilization apparatus , it is not intended to be limited to the details shown , since various modifications and structural changes may be made without departing in any way from the spirit of the present invention . for example , the total charging time t c in the embodiment of fig3 a and 4 can be further cut down by separate heating and cooling of the mass of the apparatus , and of the containers with the substance to be sterilized .