794 



HANDBOOK OF PHOTOGRAPHY 



focused on the cross rulings, and the microscope is focused in the usual waj^, which 



brings into focus the fluorescent image. 



The focal plane is different for each wavelength. The microscope was focused with 



visible light since, to enter the focal plane in the 

 ultraviolet, the tube of the microscope must be 

 racked downward and, to focus the illumination 

 as indicated by the field-of-view diaphragm, the 

 condenser must be racked upward. The bright 

 central area as seen in the searcher eyepiece will 

 not be exactly centered but should be made so by 

 adjustment of the centering condenser mount. 

 When the image is in focus in the searcher 

 eyepiece, it will also be in focus approximately 30 



cm. above. The camera is s^vung around into this position and a photograph taken. 

 Optical sections are taken bj' changing the focal adjustment mechanically by very 



small increments. This technique requires precision slow-motion adjustment of the 



Fig. 22. — Diagram showing 

 method of optical sectioning with 

 the ultra\'iolet microscope. 





V V 



' 4 



0^^ *^- ^J^) ^A i^\ ^f'\ ^^^ i^l m .^) f^^ 4 A 451 ^r:- 



J * 



^ *< ^ '4 



^Vji -^^ 



' *►• 



Fig. 23. — Optical sections of fixed but unstained mouse-tumor specimen, photographed 



on planes spaced 34 M apart. 



Fig. 24A. — A fixed specimen of tumor 

 material photographed by ultra-\aolet light. 

 (Magnification 1500 X.) 



Fig. 245. — A fixed specimen of tumor 

 material photographed by visual light 

 methods. (Magnification 1000 X.) 



microscope and accurate adjustment of all mechanical features of the microscope. 

 The slow-motion drum requires some amplification. A simple arrangement consists 

 of an aluminum counterbalanced pointer attached to the slow-motion screw and a 



