27 



In the celloidin method the imbedding mass with which the 

 spaces of the tissue are to be filled is collodion, a solution of celloidin 

 or proxylin* (soluble cotton) in ether and alcohol, hence the steps, 

 which are comparable with those of the paraffin method (see 47), 

 are (1) Dehydration, removal of the water; (2) Saturation with 

 either-alcohol, the solvent of the celloidin; (3) Infiltration with cel- 

 loidin solutions, a thin and a thick; (4) Imbedding in a thick cel- 

 loidin mass, which is hardened and (5) sections cut. 



62. Dehydration. Let it be complete, as in the prepara- 

 tion for paraffin imbedding ( 51). Immerse the tissue in 95% 

 alcohol for 12 to 24 hours or longer, changing 1 to 3 times. Consult 

 also 51 upon the dehydration of tissue. 



63. Saturation with ether-alcohol (equal parts of pure ether 

 and absolute alcohol). Remove the tissue from the strong alcohol 

 and place it in a stoppered vial of ether-alcohol for 12 to 24 hours. In 

 addition to preparing the tissue for the collodion solutions, it com- 

 pletes the dehydration, should it be imperfect. In special cases, or 

 if the dehydration is very thorough and the specimen small, this step 

 may be omitted. A satisfactory infiltration is, however, more cer- 

 tain if ether-alcohol be used. 



64. Infiltration, (a) with thin celloidin. Pour off the 

 ether-alcohol and add the thin (2%) solution of celloidin in ether- 

 alcohol. This, being a solution in ether-alcohol with which the tissue 

 is saturated, readily permeates it. It is best to allow at least a day 

 for this to take place, although if there is time a stay of several days 

 is better, there being little or no danger of deterioration while in the 

 solution. With large (1 c. c. +) objects an infiltration of a week or 

 even a month is advisable. 



Infiltration, (b) with thick celloidin. Pour off the thin col- 

 lodion solution and add thick (5 or 6%) solution (in ether-alcohol). 

 In this there is gradual concentration of the solution in the tissue. 

 Allow small specimens to remain a day, or, better, several days; 



*Celloidin is a specially prepared and purified form of pyroxylin. It is- 

 about twice as expensive as pyroxylin or soluble cotton but with it better solutions 

 can be prepared. The pyroxylin on the market seldom affords stronger solutions 

 than 8%; with celloidin a 12% solution is easily prepared. The trimmings from 

 the celloidin blocks (after the alcohol or chloroform hardening) may be dried out 

 and redissolved and thus used over and over again. Pyroxylin may be used 

 equally well. 



