ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
543 
blastoderm to the depth of about 1 /2 cm. The box is now placed in a 
tightly covered jar to prevent too rapid evaporation and the consequent 
solidification of the collodion. After the blastoderm has remained a 
sufficient length of time (from one to three or more hours, depending on 
the size of the blastoderm) in the thin solution, the collodion is removed 
with a dropper, and the thick solution poured on. After infiltrating 
sufficiently with thick collodion, 2-10 hours, open the jar and allow a 
film to form on the surface of the collodion, then fill the paper box with 
alcohol (60-80 per cent.) and allow it to remain till the collodion 
becomes firm and tough ; 2-4 hours is usually sufficient. Now with a 
sharp knife a square or rectangular piece ot collodion including the 
blastoderm is cut out and arranged on the cork in any position desired ; 
the block is fastened to the cork, as any ordinary tissue, by simply 
pouring over it thick collodion, which is hardened by immersing in 
alcohol (60-80 per cent.) for from 5 to 15 hours. 
For holding the corks under the alcohol the following apparatus has 
been found more economical and convenient than the method of attaching 
Fig. 67, jar for hardening the collodion of collodion-imbedded objects. P, plaster 
of Paris disc, in which are imbedded the glass tacks. The cork C, on which the 
embryo E is imbedded, is pushed down upon a glass tack T, and is held in position 
under the liquid L, alcohol or chloroform, while the collodion is hardening. Fig. 68, 
ether wash-bottle for blowing ether vapour upon collodion or celloidin sections to 
fasten them to the side. The tube of calcium chloride (CaCl 2 ) is for dehydrating 
the ether vapour. 
weights to the corks. The apparatus consists simply of a glass jar, in 
the bottom of which are fastened several rows of glass tacks. The 
materials necessary for its construction consist of a wide-mouthed jar, 
a few pieces of glass rod, and a little plaster of Paris. The tacks are 
made by beating the glass rod and drawing it out to a rather sharp 
Fig. 67. 
Fig. 68. 
