280 
PROCEEDINGS OF THE SOCIETY. 
friend to verify the maker’s statement that it would resolve the A. 
pellucida , which it did clearly and beautifully, using Zeiss comp, ocular 
27 to obtain sufficient amplification to enable the resolution to he seen 
with my hypermetropic and somewhat presbyopic eyes. In order to test 
this matter still farther, I requested the Gundlach Optical Co., of 
Rochester, N.Y., to make me a low-power cheap lens with similar 
corrections. This they effected in a 3/4 in. Ang. Aper. 38° ; I enclose 
specimens of its work. 
A further test of the principle involved was carried out by the 
Gundlach Co. by the construction of an ordinary photographic lens of 
13 in. equivalent focus, but corrected specially for yellow light. I 
enclose two samples of its work, copy of an oil painting and a photo- 
graph showing the under surfaee of the horse- foot crab. 
I think it will be admitted that up to the time of the late Colonel 
Woodward photomicrography was in its infancy. The superb work done 
by him, on the angulatum, the pellucida, the podura, and Nobert’s bands 
was a revelation. As the photographic plate of those days was sensitive 
only to the more refrangible rays of the spectrum, Colonel Woodward 
very properly insisted that the best work could only be accomplished by 
the use of greatly under-corrected lenses. He further insisted on the 
advantages to be derived from a blue light filter (ammonio-sulphate of 
copper solution). This appears to have set the fashion of under-cor- 
recting lenses generally, for certainly nine- tenths of the modern lenses 
are so constructed. Now if blue sensitive plates are used, this procedure 
is undoubtedly correct, but it is at the expense, to a certain extent, of 
the visual qualities of the objective. Should a colour screen (yellow) be 
used on such a plate and with an under-corrected lens, nothing would be 
gained while the exposure would have to be very greatly prolonged. 
It seems to me therefore more philosophical to have lenses corrected 
for best visual performance, and when photographing to use plates 
sensitive to the strongest visual colour (yellow) and to employ pure 
monochromatic (yellow) light ; or if this cannot be conveniently ob- 
tained, to use the best approximation to it in the way of a properly 
coloured solution. 
I do not insist that all photomicrographic work should be done on 
yellow sensitive plates, but I do believe that these plates, with lenses 
specially corrected for them, will give better results in most kinds of 
work (especially histological) than the technique now commonly em- 
employed. 
The photomicrographs were all made by lamplight, using the 
incandescent lamp devised by the writer and described in the ‘New 
York Medical Journal,’ July 16th, 1892 (reprint herewith). 
I send an additional podura made about a year ago with a Zeiss 
2 mm. apochromatic. I do not consider it equal to the smaller picture 
made with the Spencer. 
The copy of Dr. Arnold’s old photograph will supply ammunition to 
those who believe in ‘ featherlets ’ rather than in ‘ inflations.’ ” 
On the motion of the President, votes of thanks were unanimously 
passed to Mr. Smith and to Dr. Piffard for their communications. 
