Abstract: Biocompatible reservoirs are constituted by collagen, optionally associated with mucopolysaccharides and/or gelatin; these reservoirs can be filled with an active principle which does not have to be mixed with collagen. The reservoirs can be employed to either hold or to emit one or more active principles in order to concentrate same and/or to distribute same at a controlled rate "in vitro" and/or "in vivo". The reservoirs thus are enclosed vessels of conseration of "in vitro" or "in vivo" cultures of cells, bacteria or viruses.

Abstract: The method and apparatus determines the moment when, in the course of an operation of freezing a biological body of predetermined contour, the freezing becomes complete. At the periphery of the body are implanted at least two electrodes for monitoring the impedance of the body between said electrodes. The electrodes are connected to the terminals of an impedance measuring head and of an alternating current generator. The variations of this impedance are a function of the state of freezing said body. The moment when this impedance becomes very high corresponds to complete freezing of the body between the electrodes.