498 HISTOLOGY 



for about a minute and then washed in fresh 80 per cent, to remove the 

 iodine. 



All of the reagents and stains to be used for paraffin sections may be 

 kept in a series of tube-like vials, in which the slides may be placed in 

 pairs back to back, being transferred from one vial to another. The vials 

 are kept tightly corked, and the reagents can be used for some time 

 before they must be renewed. 



In handling a large number of slides, grooved rectangular boxes are use- 

 ful. Each reagent is allowed to act, poured out and another substituted. 



Celloidin Sections. Objects imbedded in celloidin are cut with 

 either a sliding or a precision microtome, the knife edge meeting the block 

 obliquely. The block and knife are kept wet with 80 per cent, alcohol. 

 Sections are cut 10 to 15 n in thickness, and are transferred, by means 

 of a camel' s-hair brush wet with alcohol, to a dish of 80 per cent, alcohol, 

 in which they remain until wanted for staining. 



Celloidin sections are stained in a series of small, shallow staining 

 dishes. The sections are taken from 80 per cent, alcohol and transferred 

 through graded alcohols to water or the solvent of the stain. If deposits 

 of corrosive sublimate are present and were not removed before imbedding, 

 the sections should be treated as directed for paraffin sections. The sec- 

 tions are transferred from dish to dish with bent metal or glass needles. 

 Celloidin sections are not treated with absolute alcohol, since the celloidin 

 would be softened. 



The handling of large numbers of celloidin sections is facilitated if 

 they are placed in a perforated cup which fits into another ordinary cup. 

 The ordinary cups contain the various reagents and the sections are trans- 

 ferred from one to another in the perforated cups. The latter may be 

 obtained as "Hobb's Tea Inf users," and lemonade cups are of proper 

 size to receive them. 



Wright's Method for Frozen Sections. This method gives permanent 

 preparations which are adequate for most routine purposes in histological 

 examination, and saves much time, labor, skill and expense. The success 

 of the method depends to a considerable extent upon the frozen sections 

 being as thin as good celloidin sections. Special automatic microtomes 

 may now be purchased, or the older form in which the sections are "chis- 

 elled" from the block will give good results if properly used. 



The tissues are fixed in 10 per cent, formalin for 12 to 24 hours or longer. 

 The piece is then trimmed so that it will present a thickness to be frozen 

 of not over 5 mm. The other dimensions of the block may be as large 

 as the freezing box of the microtome will permit. The block is rinsed in 

 water, placed on the freezing box with a few drops of water beneath it; 

 frozen and cut into sections, which should not be over 10 or 15 p- in 

 thickness. 



