LEWELLYS F. BARKER M.B., University of Chicago and Rush Medical College; FRANK J. COLE, University College, Liverpool; HENRY H. DONALDSON, Ph.D., University of Chicago; PROFESSOR LUDWIG Edinger, Frankfurt. a-M.; PROFESSOR A. Van GEHUCHTEN, Université de Louvain; C. F. HODGE, Ph.D., Clark University; G. CARL HUBER, M.D., University of Michigan; B. F. KINGSBURY, Ph.D., Cor. nell University and the New York State Veterinary College; FREDERIC S. Lee, Ph.D., Columbia University; ADOLF MEYER, M.D., Pathological Institute, New York; A. D. MORRILL, M.S., Hamilton College; G. H. PARKER, S.D., Harvard University. Annual Subscription, $3.50. PUBLISHED BY THE EDITORS, DENISON UNIVERSITY, GRANVILLE, OHIO. R. Friedländer & Son, Berlin, European Agents. THE JOURNAL OF Comparative Neurology A Quarterly Periodical Devoted to the Comparative Study of the Nervous System in all of its Aspects. EDITED BY C. L. HERRICK, Magdalena, New Mexico. ASSOCIATED WITH OLIVER S. STRONG, Tutor in Comparative Neurology, Columbia University C. JUDSON HERRICK, Professor of Zoology, Denison University. AND WITH THE COLLABORATION OF LEWELLYS F. BARKER, M.B., Professor of Anatomy, University of Chicago and Rush Medical College. FRANK J. COLE, Demonstrator of Zoology, University College, Liverpool. HENRY H. DONALDSON, Ph.D., Professor of Neurology, University of Chicago. PROFESSOR LUdwig Edinger, Frankfurt, a-M. PROFESSOR A. VAN GEHUCHTEN, Professor of Anatomy, University of Louvain, C. F. HODGE, Ph.D., Professor of Physiology and Neurology, Clark University. B. F. KINGSBURY, Ph.D., Department of Physiology, Cornell University. A. D. MORRILL, M.S., Professor of Biology, Hamilton College. G. H. PARKER, S.D., Assistant Professor of Zoology, Harvard University. THE JOURNAL OF COMPARATIVE NEUROLOGY issues one volume each year. Four numbers usually make a volume, though fascicles may appear at any time. Back numbers may be obtained at the regular rate of $3.50 per volume. Single numbers are also sold, the price varying with the contents of the number. Subscription Price $3.50 per Annum POST-FREE TO ALL COUNTRIES IN THE POSTAL UNION, Address business communications to C. JUDSON HERRICK Manager, Denison University, Granville, Ohio, U. S. A. (Entered in the P. O. at Granville, Ohio, as second-class matter.) Printed at the University Press. THE JOURNAL OF COMPARATIVE NEUROLOGY. AN ENUMERATION OF THE MEDULLATED NERVE FIBERS IN THE DORSAL ROOTS OF THE SPINAL NERVES OF MAN. BY CHARLES INGBERT. With thirty-two Figures. (From the Neurological Laboratory of the University of Chicago.) III. IV. Determination of the Areas of the Cross-Sections of the Dorsal Roots of the Spinal Nerves of Man. Determination of the Number of Nerve Fibers in the Dorsal Roots of the Spinal Nerves of Man. V. VI. VII. VIII. IX. 3. Comparison of STILLING'S Estimate with the author's Enumer- The Number of Nerve-Fibers per Square Millimeter of the Cross- The Classes of the Nerve-Fibers in the Dorsal Roots of the Spinal The Relation of the Number of Nerve-Fibers Proximal and Distal to The Application of the Numerical Results to the Innervation of the Summary. I. Introduction. This investigation was undertaken in order to ascertain the number of medullated nerve-fibers in the dorsal roots of the spinal nerves of man. It was thought that such an enumeration would assist us in determining whether we may postulate separate nerve fibers for each of the forms of dermal sensation, since it would permit us to calculate the average area of the skin innervated by a single nerve-fiber. II. Historical Statement. Attempts have been made to determine the value of the roots of the spinal and cerebral nerves as pathways for nerve impulses both by measuring the areas of their cross-sections and by estimating or counting the number of nerve fibers in them. Limiting our attention to these nerves in man we find that the area of the cross-sections of N. opticus alone has been determined by SALZER (1880)', W. KRAUSE (1880)2, and for the Nn. opticus, oculomotorius, and trochlearis by DONALDSON and BOLTON (1891)3. The determination of the number of nerve fibers was made by H. ROSENTHAL (1845)* for all the cerebral nerves except N. olfactorius, opticus, and acusticus, by estimations based on the number of fibers counted in a few squares of the ocular-micrometer. TERGAST (1872)5 made a determination of the number of nerve fibers in the N. abducens, but makes no mention of his method. KUHNT (1879) counted the number of nervefibers in a row representing the diameter of the N. opticus, and estimated the entire number by the formula r2 X 3.1416. KRAUSE (1876 and 1880)7-8 made determinations for the N. opticus, and (1880) for N. oculomotorius, but does not give his method of estimation. The area of the cross-section of the roots of the spinal nerves has been determined by KÖLLIKER (1850) and by STILLING (1859)". The only determination on record of the number of fibers. in the roots of the spinal nerves of man is that made by STILLING (1859)11. For the purpose of comparison we shall consider the determinations of the areas of the spinal nerves in detail. III. I. Determination of the Areas of the Cross-Sections of the Dorsal Roots of the Spinal Nerves of Man. Kölliker's Determination. The areas of the cross-sections of the roots of the spinal nerves, as given by Kölliker (1850)10 for a man and a woman, were in all probability obtained from fresh tissue, as no statement to the contrary can be found. The roots were sectioned between the spinal cord and the spinal ganglia at the place where they penetrate the dura mater, (i. e., near the ganglia). After removing the blood vessels and the arachnoidea, he measured the diameters of the roots, including the perineurium, and from these measurements calculated the areas of the cross-sections. That KÖLLIKER was correct in considering his results too large will be seen on comparing them with those obtained by STILLING and myself (Table I). Although the included connective tissue is the chief source of error in his results, yet the fact that he calculated the areas from the diameters of the cross-sections of the nerve roots as if they were perfect cylinders is, no doubt another source of error worth noting. Considering a Paris line (the unit which he employed) equal to 2.2558 mm., I have expressed his results in square mm. in Table I a. Although he determined the areas of the cross-sections of the ventral as well as the dorsal roots, the latter only are necessary for our comparison. 2. Stilling's Determination. The material used by STILLING (1859)" in his determination of the areas of the spinal roots was from the spinal cord of a woman, twenty-six years of age. The roots had been hardened in chromic acid according to STILLING'S method, and sectioned by hand with a razor at the place where they penetrate the dura mater. The sections, without staining, were mounted in alcohol. By means of a compound microscope and a camera lucida projections of the |