388 PREPARATIONS BY THE COLLODION METHOD [Cn. XI 



627. Infiltration with 3 % collodion. Pour off the i J % collo- 

 dion and put in its place 3% collodion. Leave the tissue in this 

 half a day or longer. 



628. Infiltration with 6 % collodion. Pour off the 3 % and add 

 6% collodion to the piece of tissue. For complete infiltration with 

 this thick collodion leave the tissue in it for one day at least. If 

 the object is large it is advantageous to leave it in for a week or two. 



629. Infiltration in strong collodion. Many workers recommend 

 as thick a solution as can be made for the final infiltration, and a long 

 stay (2-3 weeks) in the infiltrating liquid. 



Many also recommend a great many steps in the process, commenc- 

 ing with i % and gradually passing up through increasing strengths 

 till the thickest is reached. 



630. Imbedding on a cork or block. For imbedding small pieces 

 use a piece of wood (deck plug), vitrified fiber, glass, or a good cork 

 for a holder and cover the end with 6 % collodion and let it get well 

 set in the air; then put the piece of tissue on the holder and drop 8% 

 collodion upon it at intervals until it is well covered all around. 

 If one takes considerable time for this the collodion thickens greatly 

 in the air. This is an advantage, for it gives a denser block for sec- 

 tioning. After the collodion is pretty well set, place holder and tissue 

 in a vessel with chloroform to harden. One can put the preparation 

 into the chloroform, or, if the vessel is tight, it may be above the 

 chloroform, the vapor then acting as the hardener. 



631. Imbedding in a paper box. If the object is of considerable 

 size it is best to use a paper box for imbedding, as with paraffin. If 

 a very small amount of vaseline is rubbed on the inside of the box, it 

 prevents the collodion from sticking to the paper (fig. 221, 657). 



Put first some of the thick collodion in the box and let it remain 

 in the air until nearly solid, 2 to 3 minutes. Then arrange the speci- 

 men to be cut as for imbedding in paraffin, and gradually add thick 

 collodion until the object is well covered. Let the box stand for a few 

 minutes in air; then place it in a dish like a Stender dish and pour some 

 chloroform on the bottom of the dish. Cover and the collodion will 

 harden, partly by the chloroform vapor and partly by that which 

 soaks through the paper. It is well to change the chloroform at 



