Abstract: A circuit arrangement for the frequency selective analysis of the amplitudes of one or more signals in which a selective receiver is automatically scanned through a given frequency band and the scanning speed of its frequency settings is controlled as a function depending upon the difference in amplitude of signal voltages consecutively received in time and including a second selective receiver is provided which has its frequency setting changed synchronously with that of the first receiver with a constant frequency spacing between the two receivers and with the frequency of the second receiver being ahead of the first receiver and including an analysis device connected to the second receiver to derive control signals.

Abstract: A solid, adhesive-free, layered composite material consisting of two clearly defined layers, one made of membrane filters and the other of porous material, the said composite material being formed by bringing a polymeric membrane filter forming substance in its gel condition into contact with the porous material, and solidifying the said gel on the porous material; the composite material is useful as a nutrient medium carrier for microbiological tests.