INGBERT, Dorsal Roots of Spinal Nerves. 57 
no reason to think that the results of this study are appreciably 
modified by these facts. 
The 20 thick sections were stained by WEIGERT’s hae- 
motoxylin method for the medullary sheath and mounted in 
dammar. The material was obtained by the courtesy of the 
Department of Pathology, and the sections were prepared by 
Dr. Irvine Harpesty in the year Igol. 
To determine the areas of the cross-sections of the roots, 
projections of the fascicles were made on paper by means of a 
camera lucida. The areas of these projections were measured 
by means of a ConRADI planimeter. To obtain the true areas 
of the cross-sections of the roots from the areas of their pro- 
jections the magnifying power of the microscope together with 
the camera lucida used in making them was determined by pro- 
jecting a micrometer scale ruled in millimeters upon a sheet of 
paper. In doing this the micrometer slide bearing the scale 
was placed on the stage of the microscope and so projected 
that one end of the scale was in the exact center of the pro- 
jected field (as determined by a perpendicular) and the other 
end at the periphery of the field. The projected millimeters 
were marked on the paper and their length gave the magnifica- 
tion sought. The first and second millimeters from the centre 
were each magnified 68 diameters, while the third, or the one 
near the periphery, was magnified 69 diameters. 
Primary concentric circles were made on tissue paper 
through the points representing the outer ends of the projected 
first, second, and third millimeters, and six equidistant sec- 
ondary concentric circles between the outer two of the primary 
circles. The tissue paper on which were drawn these circles 
was superimposed on the projections of the roots so that the 
centre of these circles corresponded to the exact centre of the 
projected field of vision (previously determined for the pro- 
jection of the cross-section of each root) and the fascicles found 
to lie within the first and second primary circles were consid- 
ered to be magnified 68 diameters. Those fascicles the centres 
of which fell within the Ist, 2nd, 3rd, 4th, 5th, 6th, or 7th 
space (counting towards the periphery) formed by the secondary 
