161 SUMMARY OF CURRENT RESEARCHES RELATING TO 
by the sinking of the thermometer, contact is again dissolved. The 
apparatus is of small size (about 17 cm. square) and made of copper. It 
is stated not to vary more than J° during the 12 hours. 
(4) Photomicrography. 
On a Simple Method of Photomicrography by an Inexpensive 
Apparatus.* — Except for bodies of inappreciable thickness, photomicro- 
graphy will never be able to compete with accurate drawings made by 
the aid of the camera lucida. 
As the finger plays on the focusing-screw the eye is capable of 
fixing its attention on the portions of the image in sharp focus to the 
exclusion of those that are outside the focal plane, but no mere optical 
instrument is capable of doing this, and the result is that, where a body 
is of any thickness, the distinctness of the photographic image of the 
plane actually in focus is blurred, and marred by the hazy images of 
planes outside or within that plane. 
Something of the same kind is seen in ordinary landscape photo- 
graphy when lenses of long focus are employed ; either the foreground 
is blurred and the background sharp, or vice versa. Now, as the eye is 
accustomed to at once focus each object, whether near or distant, as it 
plays over a landscape, and cannot do this as it glances over the photo- 
graph, the result is unsatisfactory and unnatural. For this reason an 
enlargement from a view taken with a short focus lens, albeit it has 
special faults of its own, is often more satisfactory. 
If this be so patent in the ordinary photography of opaque objects, 
how much more unsatisfactory will be the result when, owing to the trans- 
parency of the objects, images of different degrees of sharpness are not 
merely juxta- but super-posed. Nevertheless, although for most ob- 
jects photomicrographs can never equal good drawings, especially for 
purposes of demonstration, the method presents great advantages on 
account of its facility and quickness, and is of special value in meeting 
the objections of that pestilential person, the sceptical negative observer. 
The man who, because he can find no free “ plasmodia ” in cases of 
Indian fever, refuses to believe that Laveran ever saw such bodies in 
Algeria, will be more convinced by a single photomicrograph than 
by a whole atlas of drawings. 
These latter may, or may not, be representations of the numerous 
fallacious appearances with which one becomes quickly familiar after 
working for a while at the examination of blood under high magnifica- 
tions ; but as a photograph must be a correct representation of some one 
aspect of the body, i.e. of the combination of the images of planes in 
and out of focus, its identity or otherwise with any known fallacy can 
be established in a way which is quite out of the question in the case of 
drawings. 
To be really useful, a photomicrographic apparatus should be so 
simple that it can be applied at once to the delineation of any object 
that may chance to be in the field of the Microscope ; and the difficulty 
of attaining this lies in the fact that ordinary illumination, such as is 
* By G. M. Giles, M.B., F.R.C.S., F.R.M.S., Surgeon I.M.S. Read February 
17th, 1897. 
