[ 135 ] 



^be (Brapbo^priem anb tbe ^ecbnfquc of 



Drawing fIDicroecopic anb 



HDacroecopic ©bjecta* 



By Frederick Gaertner, A.M., M.D., Pittsburgh, Pa., U.S.A. 



WITH the assistance of the Camera lucida or Grapho-prism 

 any microscopist possessing average skill in the use of 

 the pencil, may, with comparative ease and perfect 

 accuracy, reproduce the outline and principal markings of the 



object under the micro- 

 scope upon a sheet of 

 paper lying beside his 

 instrument. The sim- 

 plest and most success- 

 ful drawing-prism is that 

 of Zeiss (Fig. 1 8). This 

 is closely followed in 

 merit and popularity by 

 thatofNachet (Fig. 21), 

 then that of Abbe (Fig. 

 22), Oberhauser (Fig. 

 23),and thoseof Nobert 

 and many others, all 

 working upon the same 

 principles. 



Fig. 18. -Zeiss' Grapho-Prism. -[^he following re- 



marks and illustrations will explain and demonstrate the principle 

 of this kind of drawing apparatus. If the glass plate— ^/., Fig. 19 — 

 stands at an angle of 45^ with the axis of the eye, the rays from 

 the object {0) — which on their part also form an angle of 45*^ with 

 the glass plate, according to the position of the eye — will be 

 reflected, and the picture of the object will be seen in a position 

 which will also form a right angle with that of the object. If w. 

 (Fig. 19) is the cylinder of the microscope and /./. the piece of 

 paper, in this case the eye will see upon the paper lying beside the 

 microscope, at 0', the picture which is brought about by the trans- 



