THE CELLOIDIN METHOD 
129 
Remove the celloidin before staining by treating 10 to 15 minutes 
with ether; then wash in 95 per cent alcohol and transfer to water, 
and then to the stain. Stain to a fairly dense purple in an aqueous 
solution of Erlich’s haematoxylin; wash in dilute aqueous solution of 
calcium or sodium carbonate, and then in two changes of distilled 
water. Add a few drops of alcoholic solution of equal parts of 
Griibler’s alcoholic and aqueous safranin, and stain to a rich red. 
A dilute stain acting 1 to 2 hours is better than a more concentrated 
stain acting for a shorter time. Transfer directly to absolute alcohol, 
clear in xylol, and mount in balsam. 
Haidenhain’s iron-haematoxylin is a very satisfactory stain for 
photographic purposes. 
The celloidin method has its disadvantages as well as its advan¬ 
tages. It is extremely slow and tedious, and it is rarely possible to 
cut sections thinner than 10 n, while, on the other hand, it gives 
smoother sections. 
Succulent tissues, which are usually damaged by the paraffin 
method, are easily handled without any injury in celloidin. The 
fact that the method may be used without heat is often a further 
advantage. Stems and roots which cannot be handled at all in 
paraffin cut well in celloidin, and much larger sections can be cut than 
in paraffin, but most material of this kind can be cut without any 
imbedding. 
When material is to be imbedded, use celloidin as a last resort. 
Use paraffin when you can, celloidin when you must. 
