MICROSCOPIC MOTION PHOTOGRAPHY 109 



immersion lenses and the single microscope. It takes 

 only a moment to change. It only means sliding the 

 camera up to the first one it meshes with the light 

 trap just the same, so I use whichever method is best 

 adapted to the subject. 



Mounting a subject calls for special handling. I 

 find an excellent way is to cement with just a little 

 paraffin a glass ring about %" in diameter, and M.6 

 to i/g " thick, on the slide, put vaseline on the ring, 

 stand it on edge, and put a drop of water in the 

 lower side. Then put my subject on the cover slip, 

 invert it on the ring, the vaseline holds it tem- 

 porarily, in a moist air chamber, with a drop of 

 paraffin on either side it is ready for work and in 

 such an air chamber it will live for hours. 



Sometimes it is necessary to provide fresh water 

 continuously for subjects that require a long period 

 for development; for example, the forming of the 

 embryo in a fish egg, which took four days before it 

 hatched. This was done by first cementing a tiny 

 glass ring about \/%" in diameter and %e" high, on 

 the slide, then a large ring around it about 7/%" in 

 diameter and i/g" high, into which I had drilled two 

 holes on opposite sides. Into these holes I cemented 

 tiny funnels, bent upward, one a little higher than 

 the other, the low one leading to a beaker to catch 

 the overflow. 



