245 
Microscope”), but show it to be analogous to that of the 
Grammatophora subtilissima. Surirella gemma may truly be 
called a touchstone for a high-power objective. I do not think 
that it has been clearly defined as yet. 
Those who profess that so much can be done with ^th 
objectives in resolving Test-objects must not expect higher 
powers to verify the results they obtain. The whole art of 
testing objectives, I imagine, is in being sufficiently critical 
as to what is a fine image. The image shown of Test-objects 
by a high power of fine definition is so much more elabo- 
rated as at once to prove that the lower powers do not give 
true definition beyond a moderate magnification. For ex- 
ample, a good dth by Dallmeyer shows transverse lines on 
the Grammatophora subtilissima ; whereas, with equal magni- 
fication, but with power in the objective (as in Hartnack’s 
-jVth) rather than in the eye-piece, these transverse lines are 
seen to be the result of imperfect definition, and the surface 
appears similar to the Grammatophora marina, or P. angu- 
latum ; it is, however, much more difficult to resolve. 
It has been said that objectives which give the best results 
on Nobert’s Test-lines and on Test-diatoms necessarily give 
inferior images of Podura scale. It is quite certain that the 
more powerful objectives — those giving greater magnification 
and definition — do not give so flattering an image of Podura 
scale as is given by a good -|4h. But the fault, if anywhere, 
is in the object, not in the objective. Podura scale is as fine 
a test as any for a ^th, but not for the higher powers. 
In conclusion, I would suggest that the Society should 
improve the collection of Test-objects in its possession, and 
specially that we should have one of Nobert’s new Test- 
plates, so that the Fellows may try their objectives on a 
standard test of this kind. 
On the Identity of the White Corpuscles of the Blood 
with the Salivary, Pcs, and Mucous Corpuscles. By 
Joseph G. Richardson, M.D., Formerly Resident Phy- 
sician at the Pennsylvania Hospital. 
The nature of the nucleated corpuscles so abundant in the 
saliva has long been a subject of some uncertainty, and 
although they have probably, as favorite test objects for the 
higher powers, been more frequently examined by microsco- 
pists than almost any other constituent of the glandular 
secretions, observers seem to have been generally contented 
