lOO 



with paraffin heat is required, with collodion no heat ; (2) paraffin 

 must be removed from the sections subsequently, collodion need not 

 and usually is not dissolved out ; (3) by the paraffin method may 

 be obtained small sections (2 cm. square or less), and thin, by the 

 collodion, larger sections, but thicker. With paraffin heat (melting 

 and cooling) is necessary, and the mass is sometimes spoken of as a 

 fusion imbedding mass ; collodion is a solution, and the mass is left 

 in the tissues by evaporation or its equivalent. 



In the collodion method the imbedding mass with which the 

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

 lin (soluble cotton) in ether and alcohol, hence the steps, which are 

 comparable with those of the paraffin method (see § 41), are (i) 

 Dehydration, removal of the water ; (2) Saturation with ether-alco- 

 hol, the solvent of the collodion ; (3) Infiltration with collodion 

 solutions, a thin and a thick ; (4) Imbedding in a thick collodion 

 mass, which is hardened and (as employed in this course) clarified 

 and (5) sections cut. 



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

 tion for paraffin imbedding (§ 43). Immerse the tissue in 95% 

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

 § 43 upon the dehydration of tissue. 



§ 52. Saturation with ether-alcohol (equal parts). Re- 

 move the tissue from the strong alcohol and place it in a vial of 

 ether-alcohol for 1 2-24 hours. In addition to preparing the tissue 

 for the collodion solutions, it completes 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 certain if ether-alcohol 

 be used. 



§ 53. Infiltration : (a) with thin collodion. Pour oflF the 

 ether-alcohol and add the thin {1}^%} solution of collodion (§ 154). 

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

 urated, 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 (i c. c. -f ) objects an infiltration of a week or 

 even a month is advisable. 



§ 54. Infiltration : (b) with thick collodion. Pour ofi" the 



