Studies of the activity of single reticular neurones have shown that many kinds of fibres converge upon them and influence them (Mollica, Moruzzi & Naquet, 1953; Baumgarten, Mollica & Moruzzi, 1954 Brodal, 1957). Although each group tends to be concentrated in certain areas they are intermingled, and so a knowledge of the position of an electrode tip is of little use in indicating cell type. A logical development of micro-electrode work in this region of the brain is a search for these types, followed by a study of their properties. In the present series of experiments reticulospinal (RS) neurones have been identified and their response to cutaneous and muscle afferent stimulation has been examined. Part of this work has been briefly reported (Wolstencroft, 1961(Wolstencroft, , 1962.
METHODSExperiments were made on thirty-nine cats weighing between 1-8 and 4-5 kg. They were decerebrated under ether or halothane (Fluothane, I.C.I.) anaesthesia, which was then discontinued. In all experiments the brain stem was cut between the colliculi and the rostral portion of the brain removed. In some experiments the common carotid arteries were clamped during and for 10 min after the section, the clamps then being removed. In the majority of experiments, in order to reduce blood loss, a form of anaemic decerebration was carried out before section of the brain. This was done after removal of a length of trachea and oesophagus and exposure of the ventral surface of the pons and medulla by removal of the overlying bone. The basilar artery was ligated at the rostral end of the exposure and the external carotid arteries ligated just distal to the origin of the lingual artery. In a few experiments the ascending pharyngeal arteries were also ligated, but this was discontinued after it was found that it made little difference to blood loss. This procedure is simpler than * Present address.