Evidence obtained from simple chemical tests suggests that the black deposit in Golgi-Cox impregnated nerve cells which have been submitted to alkalinisation is black mercuric sulphide. Some sulphydryl and disulphide containing compounds may prove to be useful chemical models for studying the mechanism of this histological method.

Slabs of cat parietal cortex with some 2 mm of underlying white matter were surgically isolated from the rest of the nervous system, without interference with the superficial blood supply. Wire micro-recording electrodes were inserted into the isolated cortex; bone, muscle and skin wounds were repaired and the animal allowed to recover from anaesthesia. The adequacy of surgical isolation was examined histologically 8--12 weeks after operation. Only one of the six preparations reported here showed surviving neural connections with the rest of the brain. Soon after operation, spontaneous bursts of neural activity appeared within the isolated area. These became more frequent until neural discharge was continuous but irregular. Our records were made from this time onwards. The interval distributions obtained from neurons within the isolated area did not differ significantly from log-normal curves. When the unrestrained animal fell asleep, there was no significant alteration in the model interval or geometric standard deviation of interval distributions recorded from cells in isolated cortex. The interval distributions of neurons in isolated cerebral cortex resembled those of neurons in the intact cortex of an alarmed animal. It is concluded that the reduction of modal interval that is shown by neurons in intact cortex when an animal falls asleep is probably due to the neural influence of infracortical structures.

La méthode décrite permet des enregistrements extracellulaires de l'activité de neurones corticaux chez le chat totalement libre. On retient les résultats suivants: 1.1. Des enregistrements unitaires peuvent être poursuivis pendant des périodes allant de un jour à plusieurs semaines.2.2. Ils ne sont perturbés par aucun des mouvements normaux de l'animal.3.3. Des enregistrements simultanés peuvent être effectués à partir de diffeérents niveaux.4.4. La croissance normale du chat peut agir comme une ‘micromanipulation’ naturelle des électrodes.5.5. Rien ne semble s'opposer à ce que la méthode soit appliquée à autres niveaux du cerveau et à d'autres espéces.

Some methods of micro-electrode tip position marking are briefly discussed. Alcian blue, extruded iontophoretically with low current intensities (0.5 μA) and short time intervals (1–2 min) produces well-defined, non-fading spots in nervous tissue. We have succeeded in producing 45 spots in 54 attempts. Les auteurs décrivent briévement plusieurs méthodes de marquage de la position de l'extrémité d'une électrode. Le bleu Alcien extrait par ionophorése avec des intensités de courant faibles (0.5 μA) et des intervalles de temps courts (1–2 min) produit dans le tissue nerveux des taches bien défines et ne s'effaçant pas. Nous avons réussi á produire 45 taches en 54 essais.