Making Sections 159 



12 slides have passed through. It must be remembered that paraffin is 

 completely insoluble in the alcohol used to remove the xylene, so that it 

 is of no use to soak a slide in a solution of wax in xylene and imagine that 

 it will be sufficiently free from wax for subsequent staining. Some people 

 use three jars, the first two containing xylene and the third having a mix- 

 ture of equal parts of absolute alcohol and xylene, to make sure that all 

 the wax is removed. If even a small trace of wax remains, it will prevent 

 the penetration of stains. Assuming that one is proceeding along the 

 classic xylene-alcohol series, the slide is then passed from either the 

 fresh xylene or the xylene-absolute alcohol mixture to a coplin jar of 

 absolute alcohol. It is unfortunate that as yet nobody seems to have placed 

 on the market a coplin jar or slide-staining dish that has a lid which fits 

 tightly, since absolute alcohol, which is very hygroscopic, is rarely of 

 much use after it has been left on an open bench for a day or two. It 

 does not matter much if xylene is carried over into the absolute alcohol, 

 but as soon as the first trace of a white flocculent precipitate appears in 

 the alcohol— indicating that some wax is being carried over— it must be 

 replaced by fresh alcohol. 



The author never bothers to use a series of graded alcohols between 

 absolute alcohol and water. These graded series are necessary, of course, 

 when one is dealing with the dehydration of whole objects that may be 

 distorted, but the author has never been able to find the slightest differ- 

 ence in a thin section between one that has been passed from absolute 

 alcohol to water and one that has been graded laboriously down through 

 90 per cent, 80 per cent, etc., the length of the series varying with the 

 wishes of the individual. As soon as the slide has been in water long 

 enough to remove the alcohol, it should be withdrawn and examined care- 

 fully to make sure that it has been sufficiently dewaxed. If the water 

 flows freely over the whole surface, including the sections, it is safe to 

 proceed to staining in whatever manner is desired. If, however, the sec- 

 tions appear to repel the water or there is even a meniscus formed around 

 the edge of a section, it is an indication that the wax has not been re- 

 moved and that the slide must again be dehydrated in absolute alcohol, 

 passed back into a xylene-alcohol mixture, and thence again into pure 

 xylene. 



In the specific examples in Part Three, descriptions are given of indi- 

 vidual staining methods. The purpose of this chapter is to discuss only 

 the general principles involved. 



It is assumed that the sections will be mounted in a solution of dried 

 balsam in xylene. The slide is removed from the xylene, drained, and 

 placed on any convenient flat surface. A drop of the mountant is taken 

 from the bottle and liberally dropped over the surface of the sections. A 



