PHO TO-MICROGRAPHY 



[CH. VIII 



Bi-EITTi 











IWl li HtWI Ill-unit^ 



■^ ; 1 < 





g. ""■ 





§281. Arranging the Embryos.— As usually prepared the 

 embryos are white and therefore require a dark background. This 

 may be attained either by placing the embryos in a dark dish or on 

 some paper blackened with water-proof India ink, or by putting them 

 in a glass vessel like a Petri dish with a piece of black velveteen on 

 the stage below. Black glass on the bottom of the dish containing 

 the embryos etc., forms one of the best dark backgrounds. The 

 specimens will of course be in a liquid, usually alcohol. 



Fig. 167-178. Leitz Micro- 

 summar Objectives of 64 and 42 

 mm. focus. {Cuts from Leitz 

 Photomicrographic catalog). 



If several embryos are to be taken at once, they are arranged 

 in rows something as the . words on a line. Arrange them in 

 even vertical as well as horizontal rows so that when the print is 

 made it will be easy to cut them apart. When the embryos are 

 arranged, one should be certain that the light brings out the details 

 most desired. For example, if one is photographing an embryo 

 which shows the branchial pockets well, great pains should be taken 

 to so arrange the embryo with reference to the light that the proper 

 shading will be given to bring out the gill pockets most emphati- 

 cally. One can learn to do this only by practice. It is advanta- 

 geous to have an assistant, then while the operator is, looking into 

 the camera the assistant can turn the embryo in various directions 

 until the appearance is most satisfactory. 



§ 282. Focusing. — For getting a general focus, and for the 

 general arrangement the ground glass screen is used, but for the 

 final focusing it is desirable to use a focusing glass. 



The tripod microscope answers fairly well for a focusing glass, 

 but several are now made with much more perfect corrections and 

 for photo-micrography it is desirable to have as good apparatus as 

 can be obtained. For using the focusing glass one may have a clear 

 glass screen and set the focusing glass upon it. There should be a 

 diamond cross in the middle of the screen on the under side where 

 the ground surface usually is and this surface of the glass like that 



