dredths of a second shorter on cold winter days (Vintschgau apud Exner, Hermann's Hdbh., p. 270). Intoxicants alter the time. Coffee and tea appear to shorten it. Small doses of wine and alcohol first shorten and then lengthen it; but the shortening stage tends to disappear if a large dose be given immediately. This, at least, is the report of two German observers. Dr. J. W. Warren, whose observations are more thorough than any previous ones, could find no very decided effects from ordinary doses (Journal of Physiology, vi. 311). Morphia lengthens the time. Amyl-nitrite lengthens it, but after the inhalation it may fall to less than the normal. Ether and chloroform lengthen it (for authorities, etc., see Buccola, p. 189). Certain diseased states naturally lengthen the time. The hypnotic trance has no constant effect, sometimes shortening and sometimes lengthening it (Hall, Mind, vш. 170; James, Proc. Am. Soc. for Psych. Research, 246). The time taken to inhibit a movement (e.g. to cease contraction of jaw-muscles) seems to be about the same as to produce one (Gad, Archiv f. (Anat. u.) Physiol., 1887, 468; Orchansky, ibid., 1889, 1885). An immense amount of work has been done on reactiontime, of which I have cited but a small part. It is a sort of work which appeals particularly to patient and exact minds, and they have not failed to profit by the opportunity. CEREBRAL BLOOD-SUPPLY. The next point to occupy our attention is the changes of circulation which accompany cerebral activity. All parts of the cortex, when electrically excited, produce alterations both of respiration and circulation. The bloodpressure rises, as a rule, all over the body, no matter where the cortical irritation is applied, though the motor zone is the most sensitive region for the purpose. Elsewhere the current must be strong enough for an epileptic attack to be produced.* Slowing and quickening of the heart are also observed, and are independent of the vaso-constrictive phenomenon. Mosso, using his ingenious 'plethysmo * François-Franck, Fonctions Motrices, Leçon xxII. graph' as an indicator, discovered that the blood-supply to the arms diminished during intellectual activity, and found furthermore that the arterial tension (as shown by the sphygmograph) was increased in these members (see B wwwwww FIG. 23.-Sphymographic pulse-tracing. A, during intellectual repose; B, during intellectual activity. (Mosso.) Fig. 23). So slight an emotion as that produced by the entrance of Professor Ludwig into the laboratory was instantly followed by a shrinkage of the arms.* The brain itself is an excessively vascular organ, a sponge full of blood, in fact; and another of Mosso's inventions showed that when less blood went to the arms, more went to the head. The subject to be observed lay on a delicately balanced table which could tip downward either at the head or at the foot if the weight of either end were increased. The moment emotional or intellectual activity began in the subject, down went the balance at the head-end, in consequence of the redistribution of blood in his system. But the best proof of the immediate afflux of blood to the brain during mental activity is due to Mosso's observations on three persons whose brain had been laid bare by lesion of the skull. By means of apparatus described in his book, t this physiologist was enabled to let the brain-pulse record itself directly by a tracing. The intra-cranial blood-pressure rose immediately whenever the subject was spoken to, or when he began to think actively, as in solving a problem in mental arithmetic. Mosso gives in his work a large number of reproductions of tracings which show the instantaneity of the change of blood-supply, whenever the mental activity was quickened by any cause whatever, intellectual * La Paura (1884), p. 117. Ueber den Kreislauf des Blutes im menschlichen Gehirn (1881). chap. I. The Introduction gives the history of our previous knowledge of the subject. or emotional. He relates of his female subject that one day whilst tracing her brain-pulse he observed a sudden rise with no apparent outer or inner cause. She however confessed to him afterwards that at that moment she had caught sight of a skull on top of a piece of furniture in the room, and that this had given her a slight emotion. The fluctuations of the blood supply to the brain were independent of respiratory changes,* and followed the quickening of mental activity almost immediately. We must suppose a very delicate adjustment whereby the circulation follows the needs of the cerebral activity. Blood very likely may rush to each region of the cortex according as it is most active, but of this we know nothing. I need hardly say that the activity of the nervous matter is the primary phenomenon, and the afflux of blood its secondary consequence. Many popular writers talk as if it were the other way about, and as if mental activity were due to the afflux of blood. But, as Professor H. N. Martin has well said, "that belief has no physiological foundation whatever; it is even directly opposed to all that we know of cell life." A chronic pathological congestion may, it is true, have secondary consequences, but the primary congestions which we have been considering follow the activity of the brain-cells by an adaptive reflex vaso-motor mechanism doubtless as elaborate as that which harmonizes bloodsupply with cell-action in any muscle or gland. Of the changes in the cerebral circulation during sleep I will speak in the chapter which treats of that subject. CEREBRAL THERMOMETRY. Brain-activity seems accompanied by a local disengagement of heat. The earliest careful work in this direction was by Dr. J. S. Lombard in 1867. Dr. Lombard's latest results include the records of over 60,000 observations. He noted the * In this conclusion M. Gley (Archives de Physiologie, 1881, p. 742) agrees with Professor Mosso. Gley found his pulse rise 1-3 beats, his carotid dilate, and his radial artery contract during hard mental work. + Address before Med. and Chirurg. Society of Maryland, 1879. See his book: "Experimental Researches on the Regional Tempera ture of the Head" (London, 1879). Buccola, and Beaunis. They are slow, averaging about half a second (cf. Beaunis, Recherches exp. sur l'Activité Cérébrale, 1884, p. 49 ff.). It will be observed that sound is more promptly reacted on than either sight or touch. Taste and smell are slower than either. One individual, who reacted to touch upon the tip of the tongue in 0.125, took 0".993 to react upon the taste of quinine applied to the same spot. In another, upon the base of the tongue, the reaction to touch being 0.141, that to sugar was 0.552 (Vintschgau, quoted by Buccola, p. 103). Buccola found the reaction to odors to vary from 0.334 to 0.681, according to the perfume used and the individual. The intensity of the signal makes a difference. The intenser the stimulus the shorter the time. Herzen (Grundlinien einer allgem. Psychophysiologie, p. 101) compared the reaction from a corn on the toe with that from the skin of the hand of the same subject. The two places were stimulated simultaneously, and the subject tried to react simultaneously with both hand and foot, but the foot always went quickest. When the sound skin of the foot was touched instead of the corn, it was the hand which always reacted first. Wundt tries to show that when the signal is made barely perceptible, the time is probably the same in all the senses, namely, about 0.332" (Physiol. Psych., 2d ed., II. 224). Where the signal is of touch, the place to which it is applied makes a difference in the resultant reaction-time. G. S. Hall and V. Kries found (Archiv f. Anat. u. Physiol., 1879) that when the finger-tip was the place the reaction was shorter than when the middle of the upper arm was used, in spite of the greater length of nerve-trunk to be traversed in the latter case. This discovery invalidates the measurements of the rapidity of transmission of the current in human nerves, for they are all based on the method of comparing reaction-times from places near the root and near the extremity of a limb. The same observers found that signals seen by the periphery of the retina gave longer times than the same signals seen by direct vision. The season makes a difference, the time being some hun dredths of a second shorter on cold winter days (Vintschgau apud Exner, Hermann's Hdbh., p. 270). Intoxicants alter the time. Coffee and tea appear to shorten it. Small doses of wine and alcohol first shorten and then lengthen it; but the shortening stage tends to disappear if a large dose be given immediately. This, at least, is the report of two German observers. Dr. J. W. Warren, whose observations are more thorough than any previous ones, could find no very decided effects from ordinary doses (Journal of Physiology, vi. 311). Morphia lengthens the time. Amyl-nitrite lengthens it, but after the inhalation it may fall to less than the normal. Ether and chloroform lengthen it (for authorities, etc., see Buccola, p. 189). Certain diseased states naturally lengthen the time. The hypnotic trance has no constant effect, sometimes shortening and sometimes lengthening it (Hall, Mind, vш. 170; James, Proc. Am. Soc. for Psych. Research, 246). The time taken to inhibit a movement (e.g. to cease contraction of jaw-muscles) seems to be about the same as to produce one (Gad, Archiv f. (Anat. u.) Physiol., 1887, 468; Orchansky, ibid., 1889, 1885). An immense amount of work has been done on reactiontime, of which I have cited but a small part. It is a sort of work which appeals particularly to patient and exact minds, and they have not failed to profit by the opportunity. CEREBRAL BLOOD-SUPPLY. The next point to occupy our attention is the changes of circulation which accompany cerebral activity. All parts of the cortex, when electrically excited, produce alterations both of respiration and circulation. The bloodpressure rises, as a rule, all over the body, no matter where the cortical irritation is applied, though the motor zone is the most sensitive region for the purpose. Elsewhere the current must be strong enough for an epileptic attack to be produced.* Slowing and quickening of the heart are also observed, and are independent of the vaso-constrictive phenomenon. Mosso, using his ingenious 'plethysmo * François-Franck, Fonctions Motrices, Leçon XXII. |