Method X 65 



that will fit the object-carrier of the microtome, and, with the 

 specimen well covered with thick celloidin, harden the celloidin 

 by placing the whole in a small amount of chloroform in a 

 covered vessel. Let remain till the celloidin is firm. This may 

 take anywhere from 30 minutes to 2 or 3 hours, according to 

 the size of the block of celloidin. 



The block is then put into 80 per cent, alcohol, in which it 

 may remain indefinitely. 



5. To section, use a sliding microtome. Set the knife 

 obliquely, so that, in making the section, the stroke will involve 

 two or three inches of the edge. Fasten the block in the object- 

 carrier, preferably with the longest horizontal diameter of the 

 specimen parallel to the edge of the knife, keep the block wet 

 and the knife flooded with 70 per cent, alcohol, and make sec- 

 tions 20-30 micra thick. 



Transfer the sections as cut to a dish of 70 per cent, alcohol. 

 Handle the sections entirely with a camel's hair brush. With 

 the brush wet in the alcohol each section may be easily removed 

 from the knife with a rolling wiping motion across the knife 

 toward the edge. The brush may be used without danger to 

 the edge of the knife and also, in passing from the dish of 

 alcohol to the knife, keeps the knife sufficiently flooded with 

 the alcohol. 



6. To mordant. — [a) With a pipette carefully remove the 70 

 per cent, alcohol from the sections and replace it with 50 per 

 cent, alcohol for 5 minutes. 



(b^ Replace 50 per cent, alcohol with distilled water for 

 5 minutes. 



{c) Then subject the sections to 25 or 30 cc. of the mordant 

 (B) for 4-12 hours. 



from time to time as needed. The preservation is necessarily done in alcohol, and 

 the resulting extracts from wooden or cork blocks are often injurious to the staining 

 qualities of the tissue, or at least color it. The right kind of vulcanized fiber gives no 

 extracts, sinks in the preserving fluid, and furnishes a rigid support most desirable in 

 sectioning the imbedded tissue. Vulcanized fiber, or " compressed fiber," as it is 

 sometimes called, can be obtained in boards or strips of the desired thickness and 

 may be sawn into blocks of any dimensions. The upper surface of each block may 

 be grooved with the saw so as to hold the celloidin more firmly. 



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