70 MATERIALS AND PROCESSES OF SLIDE-MAKING 



the light that, if the section is on top, a reflection of the section is seen on 

 the lower side of the slide. A diamond scratch placed in the corner is of little 

 use because it becomes invisible when the slide is in xylene. The greatest care 

 should be taken to remove all the wax from the slide before proceeding fur- 

 ther, and it is usually a wise precaution to have two successive jars of xylene, 

 passing the second jar to the position of the first and replacing it with fresh 

 xylene after about 10 or 12 slides have passed through. It must be remembered 

 that paraffin is completely insoluble in the alcohol which is 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 hav- 

 ing a mixture 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, one then passes the slide 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 which has a lid that 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 abso- 

 lute alcohol and water. These graded series are necessary, of course, when one 

 is dealing with the dehydration of whole objects which may be distorted, but 

 the author has never been able to find the slightest diffisrence in a thin section 

 between one which has been passed from absolute alcohol to water and one 

 which has been graded laboriously down through 90 per cent, 80 per cent, etc., 

 the length of the series varying upon 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 carefully 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 by whatever manner is desired. If, however, 

 the sections 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 removed 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 given in the second part of this book, descriptions 



