referring to fig1 of the drawing a portable rack 11 is illustrated with a plurality of shelves 13 . mounted on one end of rack 11 is a main air duct 16 . duct 16 may be formed of conventional sheet metal and has an opening 17 which enables coupling of the unit to an existing air exhaust source , not illustrated . opening 17 may also be formed in another location of the main or branch air ducts of shelves 13 . each of the top four shelves 13 of the rack comprises a branch air duct . this is achieved by the securing of a top shelf section 19 to a bottom shelf section 20 to provide a partially air - tight chamber therebetween . cutout 22 in each top section 19 is formed for an air - tight connection with a respective extension duct 23 that is in air - tight communication with main air duct 16 . bottom section 20 of the branch air duct has a plurality of spaced holes 25 for exhausting respective cages . each extension duct 23 has a baffle lever 27 for selectively closing off a baffle and the flow of air therethrough . animal cage 29 is of generally rectangular configuration with a bottom wall 30 that has perforations such as a grid construction 30 for the passage of air . a plurality of these cages are suspended by side flanges 31 from hangers 32 on the bottom section 20 of shelves 13 . each cage is open at its top and thus there is air communication between it and a respective hole 25 . the cages need not be in air - tight relationship with the shelves since the open grid bottom 30 of each cage will represent a substantially larger area than the small space between the cages and their shelves . this provides reasonable assurance of air flow through bottom 30 of the cage into the cage , through opening 25 , branch duct 13 , extension 23 , and into the main air duct 16 where it is exhausted . it has been found that an air exhaust of approximately 10 cubic feet per minute per cage will effectively isolate each cage without causing an uncomfortable draft on the animal . a lower air turnover rate will also work since the primary requirement is that there need merely be a negative pressure occurring in the cage in order to prevent the flow of animal odors into the laboratory room . the above - described arrangement provides a system in which the animal cages can be readily cleaned since the cage with its perforated bottom section can have an open ended waste tray 34 removably connected therewith . tray 34 may be formed from flexible sheet metal with sides 35 which grip the cage . this type of cage also enables one to use a bedding material in the cage and not encounter the normally associated problem of odor build - up . with such an arrangement the cost of cleaning will be reduced since the frequency of cleaning will not be so great . provision for a separate room for housing experimental animals becomes optional since the animal cage rack can be maintained in the laboratory room . in fact , the rack can be utilized in any room where there is an existing exhaust system and for this reason is mounted on wheels 36 . periodically , it is desirable to remove all cages and thoroughly clear the duct work of dust and hair which tend to collect and clog it . an aqueous cleaning solution may be introduced through openings 38 ( fig4 ). this fluid may be introduced under pressure and will flow the length of the duct shelf 13 . fluid will partially exit through holes 25 but most of it will flow into extensions 23 and down duct 16 . a trap opening 39 is provided in the duct 16 below the lowest shelf 13 to remove the fluid , dirt and hair .
a ventilated animal cage system is provided in which a plurality of animal cages are removably suspended on shelves of a portable rack . each shelf is hollow to form an air duct that is in communication with the cages suspended therefrom , thus minimizing the possibility of cross - contamination between animals in the cages and personnel in the laboratory room .