1892.] THE MICKOSCOPE. 115 



The Taliie of Photography to the Microseopist.— II. 



By V. A. LATHAM, F. R. M. S. 



ANN ARBOR, MICH. 



\^Co7iti7med fr07n fage ioo.'\ 



The illumination used in photography must be similar to that 

 used for eye examination. If diatom markings show best with 

 direct sunlight and oblique illumination, then they will be most 

 accurately photographed under the same circumstances. To ob- 

 tain the best results three conditions at least must be fulfilled : (i) 

 Those parts of the specimen which it is desired should stand out 

 markedly in the picture, such, for instance, as bacteria, cell nuclei, 

 etc., must be stained as deeply as possible with a color which ab- 

 sorbs the blue rays, and therefore acts on the sensitive plate just 

 like black colors, which absorb the light ; yellow and brown dyes 

 are therefore the best. To determine the suitableness of the stain 

 is to look at the stained preparation in monochromatic blue light, 

 such, for example, as may be obtained by passing the light through 

 a solution of ammonia sulphate of copper, under which condition 

 the cell nuclei, bacteria, etc., should appear as more or less black 

 bodies on a blue ground, (ii) High povver photography can best, 

 and indeed only, be obtained with sunlight, though admitting it 

 directly on the object to be photographed is disadvantageous, and 

 it therefore must be diffused by the interposition of one or more 

 plates of ground glass. 



(iii) The third condition is an illuniinating condenser of such 

 construction that the dispersed sunlight brightly illuminates the 

 object from all sides and prevents the appearance of the structure 

 picture or of ditiraction lines. No one would suspect that in these 

 conditions there are special methods of manipulation by means 

 of which it is possible to represent by photography more than 

 what actually exists. Touching up the negative of prints should 

 on no account be done, as it destroys their value. As many re- 

 touched micro-photographs are published, it is necessary to be 

 aware of the fact, and to discount them accordingly. The stains 

 usually adopted are considered the best in the order given : Bis- 

 mark brown, vesuvin or Friedliinder's ammonia carmine or 

 Piersol's modification of Schultze's stain for the nervous system, 

 chrysoidin, logwood, methyl blue, Spiller's purple, fuchsin. Car- 

 butt's blue label plates are some of the best for this work. He 

 has so improved his orthochromatic plates that no color screen is 

 required. In illumination for photography and microscopy the 

 ligJit must be kept in the direct line of the apparatus, and it is well 

 to draw the centre on the sfround-oflass focussins: screen bv draw- 

 ing two diagonals from the four corners, and the lines at intersec- 

 tion is the focal point. The best media to mount specimens in 

 for photography stand perhaps in the following order, but I have 



