518 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
conditions, by these means, yet I am fully pursuaded that sunlight is 
by all odds the best, and, for high powers, the only really satisfactory 
illumination by which to make photomicrographs that are satisfactory 
as photographs, as well as records of microscopical observations. That 
even by good lamplight fair impressions of objects under extreme 
magnification can be obtained, no one questions, but the negatives pro- 
duced by such illumination seldom, if ever, possess the characteristics 
of a really good sunlight negative, where the sharpest details are com- 
bined with an exquisite softness and harmony of half-tones. That a 
photomicrograph should be a silhouette of deep shadows and chalky 
whites, is a proposition to which I could never subscribe. Sharpness 
and vigour are, of course, the first essentials in a photomicrograph, but 
there seems to be no reason that in such a picture all the qualities of a 
good photograph should not be represented. An almost identical 
opinion regarding the advantages of sunlight, has been reached by 
Dr. R. Zeiss,* after a most exhaustive series of experiments with arti- 
ficial illuminations of all kinds, stimulated by the hope of finding a 
satisfactory substitute for sunlight, the uncertainty of which, during the 
greater part of the year, is even a greater inconvenience in Germany 
than with us. 
The third condition for good work — suitable preparations — though 
last, is by no means least, for all apparatus and illumination avail but 
little when proper preparations are wanting. Thanks to our present 
microscopical technique, these are readily obtained, since extremely 
thin and well-stained preparations of vegetal and animal tissues are now 
matters of everyday production. The thinness with which sections are 
now usually cut (’005- '01 mm.) often renders them, when stained 
with the staple carmine dyes, too actinically transparent to photograph 
well with very low powers. The interposition of some ray-filter readily 
overcomes this ; during the last three years a screen of yellowish-green 
glass has been in constant use, with the most satisfactory results, 
yielding plucky pictures of objects entirely too transparent to produce 
sufficient contrasts in the negatives ; the exposure, however, is increased 
about three to five times, but this, even when thus lengthened, seldom 
exceeds 20-25 seconds, on Carbutt’s “ B 12 ” plates. Where great 
differences of colour are present in the same preparation, or where 
certain unfavourable tints, as deep brown, prevail, the orthochromatic 
plates offer decided advantages; for, however, ordinary preparations 
with but one stain, the colour-screens, when judiciously selected, will 
yield equally good pictures, with a gain in economy, convenience, and 
certainty. The modified haematoxylin stains, producing browns and 
slate-blues, are very valuable for special purposes, but require some 
considerable technical experience for their successful production. 
What has been written may appear to discourage the undertaking of 
this most fascinating branch of photography, where the primary object of 
instructive entertainment does not warrant the acquisition of the class 
of appliances above recommended ; this should not be so, as the full 
force of these suggestions applies only to those w r hose work in this line 
necessitates the use of the higher amplifications, with the view of pro- 
ducing the highest possible results.” 
* ‘ Special- Catalog iibcr Apparate fur Mikrophotographie,’ Jena, 1888. 
