SELECTION, ETC., OF OBJECTS FOR PHOTOGRAPHING. 105 
The simplest method of spreading them is to 
place a small drop of blood on one edge of a glass 
cover, resting upon a smooth surface, and to draw 
the end of a glass slide, held obliquely, across the 
face of the cover. No pressure must be used, 
or the delicate corpuscles will be crushed and 
distorted. 
In selecting a field for photography, the aim 
should be to obtain one in which the circular form 
of the red corpuscles is preserved, in which they 
do not overlie each other, and in which one or 
more white corpuscles are to be seen. Unfortu- 
nately, an ideal field is hard to find, and the pa- 
tience of the operator will often be sorely tried 
in the effort to find one. 
The white corpuscles being larger than the red, 
and spherical in form, are very commonly drawn 
to the edge of the stain in the operation of 
spreading. Care must be taken that the blood- 
stain is quite dry and the circle of cement upon 
which the cover is to be mounted quite hard, before 
it is placed in position on the slide ; for moisture, 
or chloroform from the cement, would injure the 
preparation. 
A series of photo-micrographs of blood-cor- 
puscles, made with a standard amplification, would 
not only be interesting and instructive, but might 
also be useful for reference, to those who are called 
upon to examine blood-stains for the purpose of 
giving expert medico-legal testimony. 
The photographic method would also be useful 
for recording differences in the form and appear- 
