1887] Microscopy. 301 
plate of the instrument just below the knife, and into this tray 
the celloidin sections may be allowed to drop as fast as cut. 
he paraffine-holders are square and seven-eighths of an inch 
in diametes, so that a block of that size may very rea adily be sec- 
tioned. For the botanist, one of these holders is provided with 
a movable side and screw for clamping 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 embedded 
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 applicable for holding the corks— ` 
if properly trimmed—upon which tissues are embedded in cel- 
loidin or in gum. This style of holder also enables one to embed 
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 
series of sections without losing any essential portions. This is 
accomplished by slipping the block through the quadrangular 
clamp for the distance of half an inch every time a half-inch of 
the object 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 which 
presses against the end of the trunnion on the outside of the 
iron pillar on that side of the instrument where the knife is fast- 
- ened, so that all the sections are of exactly the same thickness 
from first to last. Cutting up large objects in the manner above 
described is not possible with any other form of microtome yet 
constructed. 
Imost any section-knife—wide- or narrow-bladed—will fit 
‘into and be firmly held by ne knife-clamp, which is, however, 
intended more especially to an ordinary razor. The best 
razors for cutting sections oe been found to be those of the 
best make only, such as Wade & Butcher, or Joseph Rodgers & 
Sons, of Sheffield. Only such razors as hold an edge well should 
e use 
For ribbon-cutting by the paraffine method the block contain- 
ing the object, after it is trimmed and soldered to the paraffine 
with which the holder is filled, by means of a heated wire, is 
covered with a thin coat of soft paraffine or “ paraffine-gum,” 
and of which “ chewing-gum’’? is made. This enables one to cut 
l t Chewing- may be rendered available for this purpose if it is melted at a — 
temperature somewhat above boiling, when the sugar which it contains 7 separate 
as caramel, leaving the pure paraffine-gum, which may be drained off and used as 
