“… It occurred to me that the artificial exposure of the brains of living animals might afford opportunity for more definite observation and further inquiry. With this idea I made numerous experiments and observations.… It was suggested to me that the perforation of the skull placed its contents in an unusual condition with regard to atmospheric pressure, and that thus an unnatural state of the circulation might be induced.… To obviate this and other possible objections, I replaced the portions of bone removed by accurately fitting watch glasses, and rendered the junction of their edges with the bone air-tight, by means of inspissated Canada balsam.… I satisfied myself of the accuracy of these observations by repeated experiments upon different animals. My experiments upon dogs were the most satisfactory; those upon rabbits least so.”--From “_Physiology of Sleep_” Guy’s Hospital Reports, Vol. VI., 1860, p. 153, &c. “The method employed by Donders and Ehrmann was the same as that employed by Durham in the experiments he made upon animals to verify the observations of Blumenbach, Caldwell, and others, on human patients.”… “The results obtained by physiological experimentation, to prove that sleep is accompanied by cerebral congestion, according to some, and according to others by cerebral anemia, are not more valuable than the results of clinical observation. Firstly, the animals upon which the experiments have been made have been wounded more or less severely, and thereby both excitement and pain have been caused; all have, therefore, necessarily been placed under pathological conditions. It is impossible to wound the head and open the skull without causing a severe shock to the system of the animals, and a more or less violent irritation of the brain; that is to say, not without producing a certain amount of pain. And we know the influence that pain can have, not only on the functions of the great organic apparatus (circulation, respiration, animal heat), but also on the anatomical and physiological state of the nerve centres. Another influence which, according to our idea, very considerably diminishes the value of the results of physiological investigation, is that sleep has always been produced by narcotics and anæsthetics in the animals submitted to experimental observations.”… “We conclude from this study that the real state of cerebral circulation, during natural sleep, does not seem to have been arrived at, notwithstanding the great number of observations and experiments lately made on this interesting subject.”--DR. MARVAUD, _Gazette Médicale de Paris_, 1878 (p. 81-2). =Eckhard, C.= M.D. Prof. Univ., Giessen. Author of “Beiträge zur Anatomie und Physiologie,” Giessen; “Die Bildung und Prüfung des Arztes;” “Experimental physiologie des Nervensystems;” “Lehrbuch der Anatomie des Menschen.”