Tue MICROSCOPE. 139 
order to avoid heating the section, as that would give it a ten- 
dency to curl; but as the melting point of the shellac is higher 
than that of the balsam, the latter may be used if thought de- 
sirable, as it may even be caused to boil without affecting the 
shellac. 
Mr. W. J. Sotas’s letter on the subject of cutting sections 
of diatoms was formally laid before the meeting. It had refer- 
ence to the paper of Dr. Flégel, read at the December meeting, 
and was also intended to be read at that meeting, but did not 
come to hand until the meeting was over, when it was informally 
communicated to those present. The letter was as follows: 
“For some time past I have been engaged in cutting sections 
of diatoms. My plan is to scrape off a green slime from our 
river mud, consisting chiefly of Pleurosigma zigzag—a large 
species suitable for cutting. The slime, together with some 
mud, unavoidably gathered at the same time, is placed in a 
saucer and covered with a piece of muslin, which lies in imme- 
diate contact with the mud, while a film of water lies above it. 
The saucer is now exposed to daylight, and the diatoms creep 
through the muslin, collecting in a consistent film on its upper 
surface. The muslin may now be lifted from the mud, it comes 
away clean bringing all the diatoms with it, but leaving the 
mud. The muslin with the diatom film is now immersed in the 
usual hardening and staining reagents. I have used a mixture 
of chromic and osmic acids and absolute alcohol for hardening ; 
borax-carmine, hematoxylin, and eosin for staining. When 
duly stained and hardened the diatom films may be removed 
from the muslin without difficulty, and cut, either by embed- 
ding in pure paraffin (melting point 58°) and mounting in 
Canada balsam, or by freezing in gelatine jelly, which allows 
one to cut consistent sections which may be mounted direct in 
glycerine on a glass slide, without passing through water. By 
employing these two processes, I have made out the internal 
structure of diatoms, and believe that I can detect fine proto- 
plasmic threads proceeding from the protoplasm that surrounds 
the nucleus and passing through apertures in the median keel. 
I am not yet, however, in a position to demonstrate this with 
absolute certainty, but hope to do so soon.” 
