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Physiological Studies of Optical Tracts
EDITORIALS
greater than the duration of the meet ing itself. It would therefore seem that the Denver course in the summer in the Rocky Mountain region and the Los Angeles course in the winter in the Pa cific Coast region both satisfy a definite need for special medical instruction and intercourse in this western country by bringing here leading American and European ophthalmologists and otolaryngologists. In this manner the west ern practitioners may have the latest developments in their specialties pre sented to them by the greatest of teach ers without too much expense or loss of time. By this arrangement the western spe cialist who finds himself in need of a vacation may in the summer time select Denver, or in the winter time choose Los Angeles for his destination, and rest assured that in either place he may satisfy both his need for recreation and learning. It is certain that everything possible will be done to maintain the present high standard of these courses so that they will be a credit to him who inspired them both, Dr. Edward Jack son. M. F. Weymann. PHYSIOLOGICAL STUDIES OF OPTICAL TRACTS A remarkable piece of work by Stephen Poliak on structure of optical tracts as studied by purely anatomical methods was described in the depart ment of Book Notices in this Journal for February, 1933 (pp. 159-160). That this-is not the only method of studying these tracts is perhaps not well known by ophthalmologists. A physiologic method based on electric reactions is a newer and very important approach to the same subject. A good abstract of this appears in Adler's new "Clinical Physiology of the Eye" (p. 175). (See p. 354 this issue for book notice). The significance of a functional study of such a structure as the optic cortex as compared to anatomical study lies in that information not available from ana tomical study may be obtained as to (1) time relations of passage of impulse over different parts of pathway, fiber cells and synapses along the pathway to
353
cortex; (2) character of response, whether single or repetitive ; what ele ments are involved, whether inhibited or facilitated by other nervous activity ; whether spontaneously active or ac tivated only by stimulation from out side ; (3) effects of drugs and anesthetics on functioning. The physiological method has been used by S. H. Bartlay and George H. Bishop in the Department of Ophthal mology of Washington University for several years past. Some of this work is reported in the American Journal of Physiology for February. This method has the advantage of being performed in a living animal and perhaps therefore more nearly approaches the normal con dition than is possible with any method of staining of dead tissue. Most of the work has been done on anesthetized rabbits though on some, only local an esthesia has been used. The stimulation of the retina by light and the measure ment of conduction to the cortex was the original intention. It was found however that there were complications in the retina, where so many possibly disturbing elements occur, that it was simpler, as a beginning, to cut the optic nerve just posterior to the eyeball and stimulate, electrically, the central end. As is well known it is possible to measure the rate of electrical conduc tion along the course of a nerve. It is known that this varies with the nerve fiber. In all nerves studied, including the optic, following a single stimulus there is just one wave in each fiber and this is not repeated. Strangely enough and as yet inexplicably, each stimulus of the optic nerves produces five waves, re corded from the optical cortex, of dimin ishing intensity, as found by Bartlay and Bishop. It has been possible to deliminate the visual cortex by the elec trical response to stimulus of the optic nerves. There is a narrow line of cleav age between the parts that will respond and those that will not. It is noteworthy that the area outlined by this physi ologic method compares fairly closely with that found by anatomical observa tions. Many points of interest have been discovered. The interpretation of some of these has thus far remained obscure.
3S4
BOOK NOTICES
For example there is a difference in time for conduction to the cortex over some pathways as compared to others. This naturally suggests intermediary synapses in the course of these bundles in which there is delayed response be cause the rate of conduction along all uninterrupted nerve fibers is the same. Significant points brought out by Bartlay and Bishop are that the optic cortex is continuously active even when the optic nerves are not stimulated ; this activity is decreased and finally stopped by anesthetics or by cutting off blood supply. Stimulation of the optic nerve increases it, causing a series of five large responses at about one-fifth second in tervals that stand out above the spon taneous activity of the cortex, but ap pear to involve the same cells. The ef fect of strychnine applied to the surface of the cortex is to cause rapid repetitive responses of large size, which propagate laterally across the cortex into the nonstrychninized area. This suggests that pathways exist from cell to cell across the cortex as well as from thalamus to cortex. The spontaneous activity of the cor tex is rhythmic, but not all cells follow the same rhythm. At any instant cer tain of the nerve pathways from one optic nerve to cortex are nonconducting or refractory, and at successive instants other pathways are refractory, while the first have recovered, so that some pathways are always available for con ducting impulses from retina to cortex. Since the cortex is continuously active without visual stimulation the act of vision must involve not simply the ar rival of impulses in the cortex, but rather an alteration by the optic nerve impulses of the continuous and spon taneous activity already going on at the cortical level. Lawrence T. Post. BOOK NOTICES Clinical physiology of the eye. By Fran cis Heed Adler, M.D. 406 pages, cloth, 92 illustrations. The Mac millan Co., New York. 1933. Price $5.00. This is an exceedingly interesting and illuminating presentation of ocular
physiology. The subject is considered exhaustively in a very readable man ner. For the first time the whole sub ject has been collected in one volume. There is a logical division into fourteen chapters with sections appropriate to each. At the end of each chapter are numerous references from the text. There is also a comprehensive alpha betical index at the end of the book. It would be difficult to speak too highly of this volume ; not only of the context but of the clear and logical manner of its presentation. Treating the subject in great detail, the author has not sacrificed readability. It is the kind of book that the reader will not want to put down. There can be no doubt that many important considerations that will be new to almost any ophthalmolo gist will be found in this volume. The author is to be congratulated on this contribution which he has made to oph thalmic literature. Lawrence T. Post. Der
Deutschen Ophthalmologischen Gesellschaft. In Leipsic, 1932. Edited by A. Wagenmann, Secre tary. Paper 8vo, 612 pages 229 il lustrations. Munich. J. F . Berg mann 1932. This volume publishes the proceed ings of the 49th meeting of the German Ophthalmological Society, formerly the Heidelberg Congress; which has been held of late years in several other Ger man cities. It contains the 65 papers read at its five sessions, the discussions of them, and 35 demonstrations given at its demonstration session. Of its 780 members there were 190 who attended this meeting, including four of the 30 who live in America. This volume has been issued within six months after the meeting, which was held May 19 to 24, inclusive. It is an up-to-date presenta tion of recent advances in ophthalmol ogyThere are eight papers on detach ment of the retina and its treatment, followed by a general discussion of the subject, in which 16 participated. Among those reading papers were Gonin, Lindner and Guist, the last two
greater than the duration of the meet ing itself. It would therefore seem that the Denver course in the summer in the Rocky Mountain region and the Los Angeles course in the winter in the Pa cific Coast region both satisfy a definite need for special medical instruction and intercourse in this western country by bringing here leading American and European ophthalmologists and otolaryngologists. In this manner the west ern practitioners may have the latest developments in their specialties pre sented to them by the greatest of teach ers without too much expense or loss of time. By this arrangement the western spe cialist who finds himself in need of a vacation may in the summer time select Denver, or in the winter time choose Los Angeles for his destination, and rest assured that in either place he may satisfy both his need for recreation and learning. It is certain that everything possible will be done to maintain the present high standard of these courses so that they will be a credit to him who inspired them both, Dr. Edward Jack son. M. F. Weymann. PHYSIOLOGICAL STUDIES OF OPTICAL TRACTS A remarkable piece of work by Stephen Poliak on structure of optical tracts as studied by purely anatomical methods was described in the depart ment of Book Notices in this Journal for February, 1933 (pp. 159-160). That this-is not the only method of studying these tracts is perhaps not well known by ophthalmologists. A physiologic method based on electric reactions is a newer and very important approach to the same subject. A good abstract of this appears in Adler's new "Clinical Physiology of the Eye" (p. 175). (See p. 354 this issue for book notice). The significance of a functional study of such a structure as the optic cortex as compared to anatomical study lies in that information not available from ana tomical study may be obtained as to (1) time relations of passage of impulse over different parts of pathway, fiber cells and synapses along the pathway to
353
cortex; (2) character of response, whether single or repetitive ; what ele ments are involved, whether inhibited or facilitated by other nervous activity ; whether spontaneously active or ac tivated only by stimulation from out side ; (3) effects of drugs and anesthetics on functioning. The physiological method has been used by S. H. Bartlay and George H. Bishop in the Department of Ophthal mology of Washington University for several years past. Some of this work is reported in the American Journal of Physiology for February. This method has the advantage of being performed in a living animal and perhaps therefore more nearly approaches the normal con dition than is possible with any method of staining of dead tissue. Most of the work has been done on anesthetized rabbits though on some, only local an esthesia has been used. The stimulation of the retina by light and the measure ment of conduction to the cortex was the original intention. It was found however that there were complications in the retina, where so many possibly disturbing elements occur, that it was simpler, as a beginning, to cut the optic nerve just posterior to the eyeball and stimulate, electrically, the central end. As is well known it is possible to measure the rate of electrical conduc tion along the course of a nerve. It is known that this varies with the nerve fiber. In all nerves studied, including the optic, following a single stimulus there is just one wave in each fiber and this is not repeated. Strangely enough and as yet inexplicably, each stimulus of the optic nerves produces five waves, re corded from the optical cortex, of dimin ishing intensity, as found by Bartlay and Bishop. It has been possible to deliminate the visual cortex by the elec trical response to stimulus of the optic nerves. There is a narrow line of cleav age between the parts that will respond and those that will not. It is noteworthy that the area outlined by this physi ologic method compares fairly closely with that found by anatomical observa tions. Many points of interest have been discovered. The interpretation of some of these has thus far remained obscure.
3S4
BOOK NOTICES
For example there is a difference in time for conduction to the cortex over some pathways as compared to others. This naturally suggests intermediary synapses in the course of these bundles in which there is delayed response be cause the rate of conduction along all uninterrupted nerve fibers is the same. Significant points brought out by Bartlay and Bishop are that the optic cortex is continuously active even when the optic nerves are not stimulated ; this activity is decreased and finally stopped by anesthetics or by cutting off blood supply. Stimulation of the optic nerve increases it, causing a series of five large responses at about one-fifth second in tervals that stand out above the spon taneous activity of the cortex, but ap pear to involve the same cells. The ef fect of strychnine applied to the surface of the cortex is to cause rapid repetitive responses of large size, which propagate laterally across the cortex into the nonstrychninized area. This suggests that pathways exist from cell to cell across the cortex as well as from thalamus to cortex. The spontaneous activity of the cor tex is rhythmic, but not all cells follow the same rhythm. At any instant cer tain of the nerve pathways from one optic nerve to cortex are nonconducting or refractory, and at successive instants other pathways are refractory, while the first have recovered, so that some pathways are always available for con ducting impulses from retina to cortex. Since the cortex is continuously active without visual stimulation the act of vision must involve not simply the ar rival of impulses in the cortex, but rather an alteration by the optic nerve impulses of the continuous and spon taneous activity already going on at the cortical level. Lawrence T. Post. BOOK NOTICES Clinical physiology of the eye. By Fran cis Heed Adler, M.D. 406 pages, cloth, 92 illustrations. The Mac millan Co., New York. 1933. Price $5.00. This is an exceedingly interesting and illuminating presentation of ocular
physiology. The subject is considered exhaustively in a very readable man ner. For the first time the whole sub ject has been collected in one volume. There is a logical division into fourteen chapters with sections appropriate to each. At the end of each chapter are numerous references from the text. There is also a comprehensive alpha betical index at the end of the book. It would be difficult to speak too highly of this volume ; not only of the context but of the clear and logical manner of its presentation. Treating the subject in great detail, the author has not sacrificed readability. It is the kind of book that the reader will not want to put down. There can be no doubt that many important considerations that will be new to almost any ophthalmolo gist will be found in this volume. The author is to be congratulated on this contribution which he has made to oph thalmic literature. Lawrence T. Post. Der
Deutschen Ophthalmologischen Gesellschaft. In Leipsic, 1932. Edited by A. Wagenmann, Secre tary. Paper 8vo, 612 pages 229 il lustrations. Munich. J. F . Berg mann 1932. This volume publishes the proceed ings of the 49th meeting of the German Ophthalmological Society, formerly the Heidelberg Congress; which has been held of late years in several other Ger man cities. It contains the 65 papers read at its five sessions, the discussions of them, and 35 demonstrations given at its demonstration session. Of its 780 members there were 190 who attended this meeting, including four of the 30 who live in America. This volume has been issued within six months after the meeting, which was held May 19 to 24, inclusive. It is an up-to-date presenta tion of recent advances in ophthalmol ogyThere are eight papers on detach ment of the retina and its treatment, followed by a general discussion of the subject, in which 16 participated. Among those reading papers were Gonin, Lindner and Guist, the last two