12 Transactions of the Society. 



II. — On Stereomicrography. 

 By G. P. Girdwood, M.D., M.R.C.S. Eng., F.K.S.C, FJ.C, &c. 



PROFESSOR OF CHEMISTRY MED. FAC. M'GILL COLLEGE, MONTREAL ; 



CONSULTING SURGEON, MONTREAL GENERAL HOSPITAL ; 



LATE ASST.-SURGEON GRENADIER GUARDS. 



(Read November 20th, 1901.) 



The beauties of the stereoscopic vision of ordinary objects, the 

 greater amount of detail which is brought out thereby, the greater 

 amount of information afforded by a stereoscopic over an ordinary 

 picture of an object, which enables the third dimension in space to 

 be appreciated, have doubtless been noticed by other workers with the 

 Microscope, and the desire to obtain a stereoscopic picture of a micro- 

 scopic object often been felt by them ; but as to how to obtain the two 

 pictures of an object viewed from different points which are necessary 

 to produce the trae stereoscopic effect, and as to methods to obtain 

 this end, if thought out by others, no one, so far as the author is 

 aware, has published anything practical. 



It occurred to the author that this might be attainable in a manner 

 somewhat similar to the plan he adopted for taking stereoscopic skia- 

 graphs by X-rays, only reversed ;* he therefore devised a small piece 

 of apparatus to adjust to his Microscope that would enable him to get 

 the necessary two pictures at an angle to the object which should 

 equal the angle of normal vision, with eyes the axes of which are at 

 a distance of 1\ in. apart and converging to a point at a focal dis- 

 tance of 12 in. 



Inasmuch as the object-glass of the Microscope is a monocular 

 apparatus and cannot be moved, it became necessary to move the 

 object itself in such a way that it should give a picture on the screen 

 of the camera, as seen by one eye, and a picture thereof taken, and 

 then to move it in such a way as to present a picture as seen by the 

 other eye, and a picture taken in the second position, taking care to 

 keep the same object or point thereof in the axis of the tube in each 

 position, and thus obtain two pictures, one of which is as seen by 

 each eye. 



If we take two points 2^ in. apart, and join them by a line, and 

 then draw lines from the two points to a third point which is 12 in. 

 from the first line, and in such a position that a line drawn therefrom 

 would bisect the first line, we should have an isosceles triangle, of which 

 the two equal sides would represent the axes of the two eyes when 

 converged upon a point at 12 in. focus. The same may be arrived 

 at by drawing a circle at 12 in. radius from a point, and selecting any 



* Montreal Medical Journal, March 1899. 



