IMBEDDING IN CELLOIDIN 267 



ing sections in this way is a slow one, and it is dit'ticult to get 

 sections as thin as ten mikrons. Therefore cellodin is to be 

 looked upon as a last resort in a difficult situation. 



Material to be imbedded in celloidin is to be prepared in all 

 respects as when paraffin is the imbedding material up to the 

 90 per cent, alcohol in the dehydrating process. From this 

 alcohol it is put into equal parts of ether and 95 per cent, alcohol 

 (which we call ether-alcohol) for several hours and then into 

 a 2 per cent, solution of celloidin in ether-alcohol, where it 

 should remain for several days and then be transferred to a 

 5 per cent, solution of celloidin in ether-alcohol, whence after 

 a few days it is to go into a 12 per cent, solution of celloidin, 

 and after it has remained here a few days longer it is ready 

 to be mounted on a pine block preparatory to being sectioned. 



Prepare a pine block large enough in cross-section to sup- 

 port the material and with other dimensions adaptable to its 

 being clamped in the object carrier of the microtome. Leave 

 one end of the block rough and soak this end in ether-alcohol 

 for a while and then dip it for a moment in the 2 per cent, cel- 

 loidin solution. Remove the material from the thick celloi- 

 din and set it in right position on the prepared end of the block. 

 Let the celloidin on the block stiffen for a moment only and 

 then dip the celloidin end into the thick solution, remove it 

 and hold it upright so that the new coating of celloidin may 

 spread out somewhat over the end of the block and make a 

 solid union, and as soon as the celloidin has hardened a little 

 at the surface drop the preparation into a dish of chloroform. 

 After the celloidin has hardened in the chloroform for a day 

 put the preparation into equal parts of glycerine and 95 per 

 cent, alcohol where it is to remain until wanted for sectioning. 



If it is more convenient to obtain ordinary collodion or gun 

 cotton in place of celloidin it will do just as well as the latter. 



When wood tissue is to be imbedded in celloidin it has been 

 found helpful first to boil it thoroughly to drive out the air, 

 then to soak it for about two weeks in equal parts of commer- 

 cial hydrofluoric acid and water, or in stronger solutions up to the 



