1887. ] MICROSCOPICAL JOURNAL. se Fb 
at one point, and the pawl which catches into the notches in the toothed wheel 
being released at any desired point by the action of the adjustable sector, it 
is possible to adjust the apparatus with great accuracy for cutting sections of 
any desired thickness. If a given radius of the wheel is moved through the 
are embraced by a single tooth, sections are cut having a thickness of only 
tooo Of an inch, or .0o25 mm.,—a thickness which is only practically pos- 
sible with parafline embedding and a very keen razor. If more teeth are 
taken by the pawl, any thickness of section is possible up to about ;1, of an 
inch, or .0625 mm. 
Gy 
A freezing attachment, which has lately been appended to the apparatus, 
shows that frozen sections can be made with as great rapidity and success as 
those cut from objects embedded in the paraffine block, and very nearly, if 
not quite, as thin. The freezing attachment is as simple and efficient as the 
self-adjusting and cutting devices of the instrument. Other auxiliary appa- 
ratus makes it possible to cut celloidin sections. This is effected by means 
of alcohol conducted by a tube from a reservoir to the knife, over which the 
fluid will run and drain into a tray below in such a way as not to come in 
contact with any other parts of the machine. This tray fits into a recess in 
the side of the bed-plate of the instrument just below the knife, and into this 
tray the celloidin sections may be allowed to drop as fast as cut. 
The paraffine-holders are square and seven-eighths of an inch in diameter, 
so that a block of that size may very readily be sectioned. For the botanist, 
one of these holders is provided with a movable side and screw for clamp- 
ing objects, so that rather tough stems may be firmly held between blocks of 
cork, while the more delicate vegetable tissues, or such as must be imbedded 
in fresh carrot, soaked in gum and hardened in alcohol, may also be firmly 
held for sectioning by the same device, provided the pieces of carrot are first 
trimmed into the right shape. The same style of holder is equally applica- 
ble for holding the corks—if properly trimmed—upon which tissues are em- 
bedded in celloidin or in gum. This style of holder also enables one to em- 
bed very long objects entire in paraffine,—such as earth-worms,—and to cut 
them as a single piece, provided the surrounding paraffine is carefully 
trimmed so as to have two opposite sides parallel. An object six inches long 
and three-fourths of an inch in diameter embedded in this way may be cut 
into an absolutely continuous series of sections without losing any essential 
portions. This is accomplished by slipping the block through the quadran- 
gular clamp for the distance of half an inch every time a half-inch of the ob- 
ject has been cut off in the form of sections. One-half inch is the length of 
block which can be cut at one time without readjusting the feed-screw which 
moves the block and vibrating lever over towards the knife, the whole being 
kept firmly in place against the face of the hollow screw by a strong spring 
