THE PROJECTION OF THE OLFACTORY EPITHELIUM ON THE OLFACTORY BULB IN THE RABBIT

In a previous study (Le Gros Clark and Warwick, 1946) the degeneration of olfactory receptors in the rabbit following complete or partial ablation of the olfactory bulb was examined by reference to sections of the mucosa covering the septal cartilage, stained by Bodian's protargol method. Evidence was advanced to show that this is a true secondary degeneration following interruption of the primary olfactory neurons, and not the result of other factors such as vascular disturbance. It was found that the degeneration of the olfactory receptors occurs with great rapidity, for they undergo almost complete disintegration one week after removal of the bulb. The atrophy of the receptors is associated with a shrinkage in depth of the whole epithelium. The histological picture of the septal epithelium following partial lesions of the bulb incidentally led to the conclusion that there is no definite localized projection of different areas of the olfactory epithelium on to the bulb, for such lesions appeared to lead to a general thinning out of the receptors rather than to localized areas of complete degeneration. Later, evidence was brought forward by Adrian (1950), on the basis of electrophysiological studies, that there is in fact some degree of localized projection, though of a rather diffuse kind. He further made the interesting suggestion that this may have some importance as a basis for olfactory discrimination. It therefore appeared desirable to investigate the problem further by experimental anatomical methods, without limiting observations to a restricted area of the septal mucosa. As will be seen, this more extended enquiry has provided definite evidence of a general type of localization in the projection of the olfactory epithelium on the olfactory bulb.