Analysis of particles flowing in a fluid

An inventive apparatus for the analysts of particles dispersed in a flowing fluid with an illuminating device, a detecting device and an evaluating device, in which the illuminating and detecting devices are so constructed that in the particle flow they define a measuring volume with a cross-section varying in the flow direction over the height thereof, and in which the evaluating device is so constructed that it only permits further evaluation of those particles, whose measured transit time exceeds a predetermined minimum signal duration, provides for the lateral surfaces of the measuring volume to have a construction changing in continuously concave manner. (Figure 3 illustrates the measurement volume).