CH. VIII.} 



PHO TO-MICROGRA PHY. 



193 



many workers find the only opportunity for work. Following the sunlight, the 

 electric light is the most intense of the available lights. Then conies magnesi- 

 um, the lime light, the gas-glow or Wellsbach light, and lastly, petroleum 

 light. The last is excellent for the majority of low and moderate power work. 

 And even for 2 mm. homogeneous immersion objectives, the time of exposure is 

 not excessive for many specimens ( \%. to 3 minutes). This light is also cheapest 

 and most available. 



Fig. 148. Vertical Photo-Micrographic 

 Camera furnished by the Bausch Csf Lomb 

 Optical Company. {From the /jth edition 

 {/S96) of their Catalog. ) 



EXPERIMENTS IN PHOTO-MICROGRAPHY. 



§ 334. The following experiments are 

 introduced to show practically just how 

 one would proceed to make photo-micro- 

 graphs with various powers, and be 

 reasonably certain of fair success. If 

 one consults prints or the published 

 figures made directly from photo-micro- 

 graphs it will be seen that, excepting 

 the bacteria, the magnification ranges 

 mostly beween 10 and 150 diameters. 

 The technical difficulties in making good 

 photo-micrographs of animal tissues at 

 a greater magnification are so great that, 

 ik while they may be used as the basis for 

 w figures, they are, in most cases not suit- 

 able for direct reproduction. 

 Photo-Micrographs at a Magnification of 5 to 20 Di- 

 ameters. — In the study of embryology and the morphology of small 

 animals or of individual organs like the brain, it is frequently desirable 

 to make pictures of the whole object in its natural setting. These ob- 

 jects and their surroundings are frequently from one to two centimeters 

 in diameter, that is of a size too great to be satisfactorily photographed 

 witli microscopic objectives. In common with other observers the 

 writer has found the short focus, wide angled, photographic objectives 

 to give excellent results. It is necessary to have considerable length 

 {iy 2 to 2 meters) of bellows for this, if a magnification of 10 to 15 

 diameters is desired. 



Put the objective in position in the front of the camera and place the 

 object on some kind of support near the objective. A T-shaped board 



S 335- 



