Proceedings. 69 
often most valuable. The features of the section are all there 
but in an unfamiliar aspect. One is compelled to follow out 
every detail as if for the first time. 
When a successful negative has been taken, an unlimited 
number of prints can be made from it. These prints are very 
convenient to send to other scientific workers, and they are of 
much more value as evidence than original drawings. A photo- 
graph may of course be touched up so as to conceal the truth, 
but it cannot be unconsciously falsified. 
The comparison of sections with each other is a difficult 
matter in which photography is of great service. The usual 
method is to put them one by one under the microscope. The 
details of that section which is actually being examined are 
compared with the details left in the observer’s mind from 
examination of the last section. The process is very much 
simplified if we have photographs of both sections side by side. 
The larger features can be compared as well in the photographs 
as in the preparations. The observation of finer detail must be 
checked by reference to the original, but this reference is made 
much easier when we have the photograph as a ground-plan *. 
I have purposely refrained from discussing the merits of 
photography as a method of illustrating original memoirs. In 
some cases I am convinced it will do excellent service in this 
field. In many others its want of flexibility is a hopeless 
barrier. When the author of a theory draws figures to illustrate 
his meaning, he of course lays stress on those features which 
have determined his views. Thus his drawing is a more or less 
partial statement of facts, and for that reason illustrates his 
paper better than a merely mechanical reproduction of detail. 
A certain amount of selection is possible with the camera, but 
_ only within very narrow limits. 
Turning now to the process itself, the question for the 
* Only very rough measurements can be made from photomicrographs, 
because the shrinkage of the paper on which they are printed is different-in 
different directions, so that a certain amount of distortion takes place in the 
print. This is particularly apparent in platinotype prints; less so in those 
on albumenized paper. 
