
5 
(6) When a film has formed over the exposed surface of the celloidin in the water-color 
mold transfer it carefully to a small flat-bottomed dish—a small stender dish, say—in which has 
been placed some chloroform to the depth of about 3mm. The mold containing the celloidin 
need not be submerged in this. Keep the dish tightly covered to prevent evaporation of the 
chloroform. The celloidin mass should be left in here from one to three hours, but it will 
do no harm to leave it one or two days. The chloroform vapor hardens the celloidin, giving it 
the consistency of a tough jelly. 
(ec) When the celloidin has hardened sufficiently remove it from the mold. The film of 
vaseline usually enables one to readily detach it from the inner surface of the mold. The 
celloidin cube may then be placed back into the mold and the whole placed once more in chloro- 
form vapor, where it should stay until ready to be mounted. Never let the celloidin dry out. 
(d) Take a square block of wood of a size adapted to fit the holder of the microtome. Dip 
one end into ether and hold it there for a minute or two. Then dip the moistened end into 
thick celloidin. Try to do this quickly before the ether has had time to evaporate. This end 
will then be covered with a layer of celloidin. This should be allowed to dry until it becomes 
rather firm, so that it is not readily impressed with the finger. When this has taken place, take 
the cube of celloidin containing the embedded object and with a razor take a slice off the bottom 
so as to get a clean surface. Then quickly add a drop or two of thick celloidin to the celloidin- 
coated surface of the wooden block, moisten the cut end of the celloidin cube with ether and 
press it into the still soft celloidin which has just been added to the wooden block. Hold it there 
until the celloidin has become fairly firm and then place the block in a vessel to which a little 
chloroform has been added. This will complete the hardening in an hour or two. 
- The wooden block with the celloidin cube firmly cemented to it is now thrown into 70 per 
cent alcohol, where it may remain until the operator is ready to section the embedded object. 
Before sectioning it is well to bear in mind that celloidin must never be allowed to dry. 
In my own practice I usually place two covered Syracuse watch glasses on the table next the 
microtome and in each of these I place 70 per cent alcohol. I also provide myself with a medium- 
size camel’s-hair brush with which I transfer the alcohol from one of the dishes to the knife and 
to the celloidin and remove the sections from the knife to the second dish of alcohol. 
In the work of sectioning proceed as follows: 
(a) Arrange the microtome knife obliquely, so that it will slice through the object with a 
long drawing cut for at least half the length of the blade. (See fig. 32, p. 60, in Guyer’s Animal 
Micrology, Univ. of Chicago Press, 1906.) 
(b) Remove the mounted object from the alcohol and fasten the wooden block in the 
holder of the microtome. Then adjust this holder so that the celloidin is at the proper level 
for cutting. . 
; (c) Throughout the operation keep the knife and the celloidin well flooded with 70 per 
cent alcohol. 
(d) Draw the knife through the celloidin with a straight, steady stroke. Avoid pulling 
down or lifting the knife carrier. 
’  (e) As each section is cut transfer it by means of a soft camel’s-hair brush to a dish con- 
taining 70 per cent alcohol. f he . 
(f) If the microtome is not automatic, push the knife back to position before turning the 
screw which raises the celloidin block. ; 
After the sections have been cut, the next step is to stain them. The practice here will 
vary somewhat according to the stain used. For ordinary work I prefer Delafield’s hematoxylin. 
Transfer the sections first to 50 per cent alcohol, 2 minutes. 
