referring to the drawings , in which like reference numerals refer to like elements , there is shown in fig1 a microdermal abrasion apparatus generally denoted at 10 , comprised of an abrasive supply container 12 , a handpiece 14 , a disposable waste filter 16 , an air line filter 20 and a vacuum pump 22 . waste filter 16 is comprised of a primary filter element 17 , and a secondary filter element 18 , both housed in a sealed outer container 19 . the particle supply path from container 12 to handpiece 14 is comprised of an outlet tube 24 connected to container 12 by an outlet coupler 26 , a tee - connector 28 and a particle supply line 30 , the latter connected to handpiece 14 by an inlet coupler 32 . the leg 34 of tee - connector 28 is connected to an air supply valve 36 , as described in more detail below . a waste disposal line 38 connects handpiece 14 to waste filter 16 . an outlet coupler 40 at one end of waste disposal line 38 connects to handpiece 14 . the other end of waste disposal line 38 connects to an inlet line 44 on waste filter 16 by means of a suitable fitting 42 . vacuum pump 22 provides the suction for delivery of abrasive particles to handpiece 14 and for waste removal . waste filter 16 is connected to vacuum pump 22 in any convenient or desired manner , e . g ., by a first air outlet line 46 , air line filter 20 and a second air outlet line 48 . air outlet line 46 is connected to an outlet tube 50 extending from waste filter 16 by a suitable fitting 52 . vacuum pressure may be controlled by a continuously variable air inlet valve 54 . a pressure gauge 56 may also be provided to monitor the suction at the input to pump 22 . the exhaust air from pump 22 may be exhausted to the atmosphere through a final filter / muffler 58 . as illustrated in fig1 - 3 , handpiece 14 is comprised of a cylindrical body 70 and a threadedly attached disposable tip 72 . an inlet channel 74 extending through body portion 70 provides an inlet path for abrasive particles into tip 72 , and a waste removal channel 76 extending through body portion 70 with an inlet opening 76 a in face 76 b of body 70 provides a waste disposal path for spent particles and abraded skin out of tip 72 . removable tip 72 is formed of polycarbonate or other suitable plastic material and is comprised of a hollow cylindrical portion 78 and a curved end portion 80 which may be hemispheric , parabolic or the like . an axially located treatment orifice 82 at the end of tip 72 provides access by the stream of abrasive particles to the portion of the skin to be abraded . the diameter of orifice 82 is not critical , but good results are achieved with a diameter in the range of 0 . 25 to 0 . 375 in . ( 0 . 635 - 0 . 953 cm .) handpiece body 70 may be formed teflon ® or other suitable plastic and may be molded or machined to the required shape . alternatively , handpiece body 70 may be comprised of stainless steel . the outside dimensions of handpiece 14 are not critical , but good results in terms of operator comfort and convenience are achieved with a handpiece having an overall length of less than 3 inches ( 7 . 62 cm . ), e . g ., 2 . 25 inches ( 5 . 715 cm . ), and a diameter of less than 1 . 0 inch ( 2 . 54 cm . ), e . g ., 0 . 875 inch ( 2 . 22 . 25 ). the diameters of channels 74 and 76 are also not critical , but must be sufficiently large to provide adequate particle flow with a vacuum pump 22 of reasonable capacity and power . it has also been found that the diameter of waste removal channel 76 should be larger than particle supply channel 74 . this helps promote rapid removal of spent abrasive particles and abraded skin , especially if the vacuum inside tip 72 is broken due to loss of contact of treatment orifice 82 with the skin surface . at the same time , if channels 74 and 76 are too large , the diameter of handpiece 14 must be increased , with consequent loss of maneuverability and operator comfort . given the foregoing considerations , it has been found that good results may be achieved if channels 33 and 34 are respectively 0 . 11 in . ( 2 . 794 mm .) and 0 . 80 in . ( 20 . 32 mm .) in diameter . handpiece body 70 is threadedly connected to tip 72 by external threads 84 that engage with complementary internal threads 86 on cylindrical portion 78 of tip 72 . an o - ring seal 88 is provided at the base of threaded portion 84 and engages with an unthreaded skirt portion 90 at the end of tip 72 . as previously noted , treatment orifice 82 is preferably located axially at the end of tip 72 . it has been found , however , that tissue removal is most effectively performed if the stream of abrasive particles is aimed directly at treatment orifice 82 . since channels 74 and 76 are laterally offset from the central axis of handpiece body 70 , to direct the incoming particle stream into orifice 82 , inlet channel 74 is oriented at a small angular offset from the longitudinal axis of handpiece body 70 . for a handpiece and tip having the dimensions indicated above , it has been found that the offset angle θ , as illustrated in fig3 is advantageously in the range of 3 - 4 degrees . alternatively , as illustrated in fig4 instead of angling the entire length of channel 74 , the upstream end 92 is oriented parallel to waste removal channel 76 , and only the downstream discharge end 94 of channel 74 is angled . it will , of course , be understood that the value of offset angle θ will depend on the particular dimensions of handpiece 14 and tip 72 , the important consideration being that the particle stream impinge , as nearly as possible , in the center of treatment orifice 82 . in either the configuration of fig3 or fig4 an abrasion - resistant nozzle insert 96 , fitted in a counter - bore 98 at the outlet end of supply channel 74 , may be provided , as illustrated in fig3 . the abrasive particle stream thus exits toward treatment orifice 82 through opening 96 a . microdermal abrasion unit 10 is preferably constructed with its major parts as an integrated unit . thus , supply container 12 , waste filter 16 , tertiary in - line filter 50 , vacuum pump 22 , and the various ancillary parts are all preferably mounted in a single cabinet ( not shown ). waste filter 16 and supply container 12 are preferably positioned for easy access and to facilitate removal as explained below . referring to fig6 and 7 , waste filter 16 is comprised of a cylindrical outer container 100 having a tubular body 101 permanently attached to top and bottom end caps ( fig1 and 104 ). these may be comprised of metal , plastic or heavy cardboard tube . within outer container 100 is primary filter 17 . this may be cylindrical in form and comprised of a pleated inner portion 108 over - wrapped with a flat filter paper portion 110 . alternatively , filter element 108 may be formed of a single layer , having either a pleated structure or a flat tubular structure . filter element 108 is selected to ensure trapping of the 120 micron sized abrasive particles and the abraded tissue . filter element 108 defines a boundary between a central volume 112 enclosed thereby and an exterior generally annular shaped sealed volume 114 between the filter element and the interior of outer container 100 . filter element 17 is fixed in place by cementing it to the top and bottom end caps 102 and 104 , using a potting compound or the like , before outer container 100 is assembled . top end cap 102 has openings 116 and 118 which receive air outlet tube 50 and waste inlet tube 44 sealingly connected therein . tubes 50 and 44 may be flexible plastic tubes with o . d .&# 39 ; s of ⅜ and ¼ inch respectively . tube 50 extends through opening 116 , and is connected at its end to secondary filter 18 which helps assure that there will be no venting of the waste material accumulated within waste filter 16 , even if primary filter 17 ruptures for some reason . the illustrated construction also permits disposal of secondary filter 18 without risk of exposure to the waste material . since waste filter 16 is a unitary structure , it is conveniently removable , and disposable in one piece by disconnection of tubes 50 and 44 respectively from in - line filter 20 and output channel 76 in handpiece 14 . tubes 44 and 50 are advantageously long enough to be connected together as by a fitting 42 which fits into the end of tube 50 to completely seal the container for disposal . it will be understood by those skilled in the art , however , that other forms of waste filters which permit disposal without exposure to the accumulated waste material may also be employed within the scope of this invention . referring again to fig3 a small control opening 120 is provided in tip 72 . this can be closed by the operator &# 39 ; s finger to increase the vacuum and thereby produce a more forceful stream of abrasive particles against the skin being abraded when required without adjustment of valve 54 ( see fig1 ). as will be appreciated , the same result can be obtained by placing an opening in handpiece body 70 ( not shown ) in communication with the interior of either inlet channel 74 or waste removal channel 76 . referring to fig2 and 5 , the upstream ends of channels 74 and 76 are internally tapered at 122 and 124 to receive tapered end portions of couplers 32 and 40 . coupler 32 , illustrated in fig5 is comprised of a pin 126 having a tapered end portion 128 adapted to fit into tapered end 122 of channel 74 , a flange 130 and a cylindrical rear body portion 132 taped at its end 134 , and adapted to fit into particle supply tube 30 . flange 130 provides a shoulder against which the end of tube 30 rests when assembled . ( as will be understood , tube 30 may be heated before insertion of pin 126 so that the tube contracts around rear portion 132 , thereby ensuring a tight fit . coupler 40 is similarly constructed . as will be understood by those skilled in the art , such a tapered connection ( known as a morse taper ) provides a reliable connection which can be easily made and released even under substantial internal pressure simply by twisting plug 126 . the periphery of flange 130 may be knurled at 136 to facilitate grasping for this purpose . the resulting connections are secure , but may easily be released by twisting the plug with two fingers . no tools are needed , and enlargement of the diameter of handpiece 14 to allow manipulation of the couplings is unnecessary . it should also be understood that tapered fittings as described above may be used for other parts herein which must be connected and disconnected , such as the connections between waste filter 16 and tubes 38 and 46 , the connection between vacuum pump 22 and tube 48 , etc . two factors which have been found to be important in achieving satisfactory operation are the rate and uniformity of particle flow past treatment orifice 82 in handpiece 14 . as will be appreciated , maximum particle flow rate depends in part on the capacity of vacuum pump 22 . it has been found that effective treatment can be achieved in a practical configuration using a ¼ to ½ horsepower vacuum pump providing 90 - 98 kpa uniformity of particle flow has been found to be related to the geometry of the structure of the particle flow path . this can produce rather complex effects , which in the extreme , can cause serious and frequent clogging of particle flow paths . it has been found , however , that such effects can be minimized by controlled mixing of air and particles before the particles are transported to handpiece 14 . this may be done quite conveniently at supply container 12 using any of the embodiments described below . as a result , particle flow may be made substantially uniform , and clogging largely eliminated . fig8 - 10 illustrate a preferred embodiment for particle supply container 12 . as shown , container 12 is comprised of an outer receptacle 170 having a top 168 and a bottom opening 171 sealed by a suitable closure such as an end cap 172 , a first air inlet 179 and an aeration device generally denoted at 176 . in the illustrated embodiment , aeration device 176 is comprised of a mixing chamber in the form of a tube 177 , a second air inlet 178 and a particle inlet device 180 . tube 177 extends vertically to a point adjacent to the top of receptacle 170 . a second air inlet 178 at the top of tube 177 permits inflow of air for mixing with the abrasive particles as described below . the bottom of tube 177 communicates through an opening 174 in end cap 172 with outlet coupler 26 , which , in turn , is connected by outlet tube 24 and tee - connector 28 to particle supplied tube 30 ( see fig1 ). referring again to fig8 - 10 , first air inlet 179 is provided in the top of receptacle 170 to vent the air space above the particle fill level 186 to the atmosphere . an air filter 182 is secured over air inlet 179 , e . g ., by gluing at its periphery 184 to receptacle top 168 . in use , a supply container 12 is pre - filled by a supplier with abrasive material leaving an air space 186 below the top 178 of mixing tube 176 . as will be understood , this permits air to be drawn into the tube by the suction created by vacuum pump 22 ( see fig1 ). the prefilled container is installed by removing a shipping cap ( not shown ) from the end of tube 176 and fitting 26 is attached to the tube 24 . still referring to fig8 and 10 , particle inlet opening 180 near the bottom of mixing tube 176 permits abrasive particles to enter the tube under the force of gravity and to create an air - particle mixture which is then transported through supply tube 30 to hand - piece 14 . by aerating the particles in this manner , clumping due to accumulation of moisture is prevented without the need for heaters to dry the particles or vibrations , as are sometimes employed . the dimensions of air intake opening 179 and particle inlet opening 180 in mixing tube 176 are selected to provide the desired degree of aeration . good results are achieved with an air intake opening 179 having an internal diameter in the range of 0 . 1 to 0 . 175 in . ( 0 . 445 cm . ), and preferably 0 . 125 in ( 0 . 3175 cm .) an outside diameter for tube 176 of 0 . 25 in . ( 0 . 635 cm .) and a particle inlet opening having a diameter in the range of 0 . 063 to 0 . 090 in . ( 1 . 006 - 2 . 286 mm . ), and preferably 0 . 080 in . ( 2 . 032 mm .). further adjustment of the aeration maybe achieved by use of valve 36 connected to leg 34 of tee - connector 28 . by opening valve 36 , more air is introduced to supply tube 30 , thus reducing the quantity of abrasive particles . this allows continuous and infinite adjustment of the particle flow rate . in a practical application , the capacity of container 12 maybe 1 - 5 pounds ( 0 . 4542 - 2 . 268 kg .). particle size is not critical , but it has been found that good results are achieved using irregularly shaped aluminum oxide particles having a maximum dimension less than about 120 microns and with sharp irregular edges . when the container is empty , it is removed and replaced by a new prefilled container . the shipping cap is reapplied to the end of tube 176 and the empty container is then discarded . fig1 - 21 illustrate several alternative embodiments for supply container 12 . the embodiment shown in fig1 differs from the embodiment of fig8 - 10 in that mixing tube 176 extends through a fitting 188 in the upper wall 189 of receptacle 170 . air enters tube 176 through an opening 191 . a protective cap 190 is provided over opening 191 . no separate air inlet such as 179 ( see fig8 ) is needed , but an air outlet hole 192 is provided near the top of tube 176 to vent air space 186 to the atmosphere . as will be understood , this is necessary to permit the particles to be drawn into particle supply opening 180 in tube 176 . the embodiment shown in fig1 differs from that of fig1 in that a separate air supply tube 194 is provided . tube 194 is mounted in a fitting 198 in receptacle end closure 172 , extends upwardly within receptacle 170 to a point above particle fill level 186 and terminates in an opening 196 . air enters tube 176 at its open top 178 and mixes with particles entering at inlet opening 180 . tube 176 terminates at a fitting 200 in closure 172 , where it may be connected directly to particle supply tube 22 ( see fig1 ). tee - coupler 28 and air valve 36 shown in fig1 are not used . instead , an in - line valve 202 in air intake tube 194 is provided to adjust air flow . the embodiment of fig1 and 14 employs a separate particle inlet tube 204 which extends through an opening 180 in a mixing tube 176 . inlet tube 180 is positioned at an angle , e . g ., 45 °, so particles entering at upper opening 206 are gravity fed through lower opening 208 and are mixed with the air stream in outlet tube 176 . in the embodiment of fig1 - 17 , the mixing chamber and the outlet device are combined . air is provided from above , as in the previously described embodiments , through a vertically extending tube 210 . tube 210 is connected at its bottom end to a funnel 212 which terminates in a spout 214 , the latter being connected to outlet tube 24 ( see fig1 ). abrasive particles are gravity - fed into spout 214 by a particle feed device generally denoted at 216 , which is comprised of a circular trough 218 that surrounds tube 210 . trough 218 is open at the top and is comprised of a side wall 219 and an annular bottom plate 220 . outlet tubes 222 connected to openings 224 in trough bottom 220 feed into spout 214 through openings 226 . as will be understood , the constructions shown in fig1 - 14 and fig1 - 17 may be used instead of the tubular mixing chambers and particle inlet devices in any of the embodiments shown in fig8 - 12 . in the embodiment illustrated in fig1 and 19 , a tubular mixing chamber 230 is attached to the bottom 232 of receptacle 170 . spaced holes 234 in tube 230 communicate with aligned holes 236 in receptacle bottom 232 to permit a particle inlet . alternatively , holes 234 may communicate with the interior of receptacle 170 through a slot in receptacle bottom 232 ( not shown ). air is supplied through an air inlet 236 at one end of tube 230 and mixes with particles which are gravity fed through holes 234 . the aerated mixture exits through an outlet device 238 , which may be connected directly particle supply line 30 . the air supply at inlet 236 and accordingly particle volume , may be controlled by an air valve ( not shown ). a variant of the embodiment of fig1 - 19 is shown in fig2 and 21 . here , a cylindrical mixing chamber 240 is formed at the bottom of receptacle 170 by a horizontal dividing wall 242 , including a plurality of perforations 246 by which the particles are gravity fed into mixing chamber 240 . as in the embodiment of fig1 - 19 , air is supplied at an inlet 248 through a valve ( not shown ) and the aerated mixture exits through an outlet device 250 . in summary , the present invention provides improvements in the art of microdermal abrasion including continuous variability of the particle flow rate and substantial elimination of shutdown due to clogging of the particle flow tubes , as well as improved uniformity of particle flow . in addition , the present invention provides a nozzle and input channel which direct the flow of abrasive particles toward substantially the center of the opening in the tip , thereby improving the performance of the dermabrasion process . also , the morse taper couplings employed as described in the present invention , particularly for connecting the particle supply and waste disposal lines to the handpiece , permit convenient connection and disconnection without tools , and allow the handpiece to be made small enough for convenient and comfortable use . moreover , the design of the supply container and waste filter permit disposal without risk of exposure to either clean or contaminated materials . although the present invention has been described in relation to particular embodiments thereof , many other variations and modifications and other uses will become apparent to those skilled in the art . thus , other designs for the handpiece , the disposable supply container an the waste filter are possible . similarly , the supply container need not be disposable . instead it may be constructed in a manner permitting it to be refilled upon return to the supplier . it is intended , therefore , that the scope of invention be limited not by the specific disclosure herein , but only by the appended claims .