Analogy has thus led us to conclude that this ganglion is in direct connection with olfactory impressions, and that this marks it as the point of concentration towards which they converge before being radiated towards the cortical periphery.
This simple and purely anatomic view was, for myself, to some extent a ray of light, and the real clue that enabled me to propound my theory concerning the phy siological function of the optic thalamus, by applying to the physiological interpretation of other ganglions the indisputable facts I had just ascertained respecting the anterior centre ; since it was evident that what was true for one must be true for all the other closely related centres.
Thus by successively applying the same processes of investigation I arrived at the following conclusions :*— That the middle centre, so manifestly in continuity, as regards its tissue, with the grey roots of the optic nerves, is destined for the condensation of visual im pressions (Fig. 6-13. 14.) ; that the median ganglion is connected with the condensation of sensitive im pressions (Fig. 6-3. 9.), and the posterior with that of auditory impressions (Fig. 6-3. 4.) ; and that thus, in their central order of classification, isolated sensorial impressions find independent halting-places grouped along the same line, and in an order correlatively similar to that which presides over their mode of distribution in the peripheral regions of the system.
It is, indeed, curious to observe in a human head, when examined in profile, that the olfactory organs of the nose are first met with, in the most anterior plane ; then the visual organs, the eyes, in the second line ; the sensitive organs in the third ; and finally the auditory organs, the ears, occupying the most posterior place ; and that, further, in their mode of distribution in central ganglions of the cerebral mass these same im pressions are grouped in isolated independent ganglions, occupying, as regards one another, a taxonomic order, which is in a manner only a repetition of their mode of origin in the peripheral regions (20, 13. 8. 3 Fig. 6).
These facts, which have shed quite a new light upon the anatomical and physiological functions of the optic thalami, have found their confirmation, on the one hand in the experiments of physiology, and on the other hand in the clinical examination of symptoms, which are in these matters the irrefragable criterion of every truly scientific doctrine.
Thus Dr. Edouard Fournie, in a series of experiments made on living animals by means of the injection of irritating substances into different parts of the optic thalamus, succeeded in annihilating such or such sen sorial impressions, according as the traumatic laceration had attacked such or such a ganglion of the optic thalamus. Thus he succeeded in successively annihi lating vision, sensation, smell, etc.* On the other hand, well-observed clinical facts, re ported by former writers, and therefore much anterior to my own researches, showed me that sometimes sen sorial impressions might be totally and successively destroyed when the two optic thalami were simulta neously attacked, and that sometimes isolated sensorial impressions might be disturbed in consequence of a local lesion of their tissue.
There exists, indeed, a typical observation made by Hunter, of which he has left a drawing, which mani festly confirms what I have just put forward.
In this observation he recounts the curious history of a young woman who, in the space of three years, successively lost the senses of smell, sight, hearing, and sensation, and who gradually sank, remaining a stranger to all external impressions. When the autopsy of her brain was made, it was found that the optic thalami of each hemisphere, and the optic thalami alone (as can be seen in the original drawing)t were attacked by a fungus hmatodes, which had progressively destroyed their substance.
In other circumstances, when circumscribed lesions have attacked separate ganglions, the abolition of such or such kinds of sensorial impressions has been noted. Thus, in three observations, for which I am indebted to the kindness of Dr. Auguste Voisin, and in which the abolition of smell on one side had been remarked, cor responding degenerations of the anterior centres weft. likewise observed.