1. Apparatus for quantitatively monitoring moving particles, comprising: (a) imaging means, disposed proximate a region to be monitored, for producing a video signal corresponding to an image of said region and of any moving particles that may be present therein; (b) signal processing means, connected to the imaging means, for processing the video signal to eliminate noise in the video signal and non-moving objects comprising the image, said signal processing means being operative to produce a filtered signal including a plurality of data points corresponding to at least a portion of the image from which the effect of both gradual variations in intensity across the image and a fixed background have been substantially reduced; and (c) counting means, connected to the signal processing means, for counting moving particles in the monitored region as a function of the relative magnitude of the data points in the filtered signal and a predetermined threshold level.