Inhaltsangabe
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1869. Excerpt: ... surrounding vegetation. From Dr. Kirk's letter, together with the fine series of specimens recently received from him at the Kew Museum, much light is thrown on the origin of the East African copals, and we hope further researches will entirely clear up this, one of the many tangled knots in Economic Botany. VELOCITY OF CEREBRAL FUNCTIONS. The "Archives des Sciences" for April 15, contains a paper by Dr. Adolph Hirsch, on M. F. C. Donders's experiments to determine "the velocity of the psychical functions of the brain," as detailed in the "Archives de Reichert et du Bois Raymond," and we extract from it the following passages:--"We know now that the brain requires about fifty-thousandths of a second to distinguish and signalize the distinction between two colours, and only fifty-thousandths of a second to distinguish between two vowels which are pronounced. What is more, M. Donders has succeeded in separating these two psychical acts into their components, and he has found that the brain employs about Vyth f a second to recognize an impression, and-th. of a second for an act of volition to signalize that the impression has been received. With regard to the rapidity of perception in cases of hearing, sight, and touch, and the duration of the functions of the cerebral organ, M. Hirsch observes, 'I endeavoured to reply to the first of these questions in 1801, and the results which I obtained for the physiological times of the different sensations have been since confirmed by eminent physiologists, amongst them M. Donders, who gives as the mean of his experiments for touch, 4-th of a second, for hearing, th, and for seeing, th. But this physiological time, as I have named the interval between the excitation, and the signal given by the manifestation of percep...
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