INTRODUCTION, 21 
the microscope and its revelations, will be likely 
to prefer the neat appearance and the sharply 
drawn lines of the latter to a photograph from 
nature. 
But for the trained eye, the photo-micrograph 
possesses special attractions; just as the photo- 
graph of a friend conveys impressions and gives 
rise to reminiscences of an agreeable nature, while 
that of a stranger is looked upon with indifference. 
The expert microscopist, also, knowing the diffi- 
culty of obtaining an ideal field free from extra- 
neous objects, and having every portion in perfect 
focus, is willing to make some allowance for slight 
defects which at once attract the attention of a 
critic who is not a microscopist. In the same way, 
the connoisseur in art in looking at a famous old 
picture learns to overlook the stains and fissures 
imprinted by the hand of time, and to his mental 
vision the work of the master is revealed in all its 
beauty, while for the untrained eye the scarred 
and dingy canvas possesses no attractions. 
By exercising great care and patience in the 
mounting of objects and in the selection of a field, 
all imperfections may be excluded except such as 
result from the physical characters of the object 
itself and the limits imposed by the laws of optics. 
In photographing with high powers, and especially 
with wide-angled objectives, it will be found that 
the slightest irregularity in the surface of an 
object makes it impossible to have all parts of the 
field in perfect focus at the same time. This is 
well shown in my photographs of Zriceratium favus 
