54 



THE ART OF MAKING MICROSCOPE SLIDES 



Stains 



fixed in Zenker's fluid (Chapter 18, F 

 3700.0010 Zenker 1894). After the speci- 

 mens have been fixed sufficiently long to 

 hold their shape when the glass plates are 

 removed, they are transferred for a 

 couple of daj^s to fresh fixative and then 

 washed in running water overnight. If 

 the crop contains any considerable quan- 

 tity of blood, it will be necessary to 

 bleach this before a satisfactory stained 

 wholemount can be made; the specimens 

 should, therefore, be transferred to the 

 bleach of Murdoch 1945 (Chapter 19, AF 

 31.1) where they should remain for a few 

 days. 



Bryozoa. Marine bryozoans may be 

 narcotized without difficulty by sprinkhng 

 menthol on the surface of the water con- 

 taining them. Subsequent fixation is best 

 in some chromic-acetic mixture, for osmic 

 acid|tends to precipitate on the test and 

 blacken the specimen. It may be pointed 

 out that, for taxonomic purposes, dried 

 wholemounts of the test prepared as 

 described in Chapter 1 are of more value 

 than are wholemounts with the expanded 

 animal. It is usually recommended that 

 fresh-water bryozoans be narcotized in 

 some cocaine solution, but the writer has 

 found menthol just as good and much 

 easier to use. Fresh-water bryozoans 

 should be fixed directly in 4% formalde- 

 hyde since they shrink badly in any other 

 fixative. 



Gastrotricha. These give excellent 

 results by the special technique for minute 

 fresh-water animals described at the 

 end of this chapter. 



Small Crustaceans. These are some- 

 times prepared as resinous mounts, 

 though the writer prefers to mount them 

 in glycerol jelly in the manner described 

 in Chapter 5. They may be narcotized in 

 weak alcohol and fixed in almost any 

 fixative. 



Other Arthropods. Wholemounts of 

 most small arthropods are better made in 

 gum media in the manner described in 

 Chapter 4. A detailed description of the 

 preparation of the skeleton of an insect 

 for mounting in Canada balsam is among 

 the typical preparations described at the 

 end of this chapter. 



Choice of a Stain 



It is now to be presumed that, whatever 

 method of narcotization and fixation has 

 been employed, the specimens to be 

 mounted have been washed free from 

 fixative and accumulated either in water 

 or 70% alcohol. The reason that so many 

 formulas and methods for staining are 

 given in Chapter 20, 21, and 23 is that no 

 two people have ever agreed on the best 

 method of staining anything. The sug- 

 gestions which follow, therefore, are hkely 

 to be modified by every individual reading 

 the book; but they are included for the 

 sake of those inexperienced in making 

 wholemounts. 



Small Invertebrates and Inverte- 

 brate Larvae, These are best stained in 

 carmine by the indirect process : that is, by 

 overstaining and subsequent differentia- 

 tion in acid alcohol. For most specimens 

 the writer prefers Grenacher's alcoholic- 

 borax-carmine (Chapter 20, DS 11.22 

 Grenacher 1879). As an alternative, 

 particularly for marine invertebrates, he 

 has frequently used the two formulas for 

 Mayer's paracarmine (Chapter 20, DS 

 11.22 Mayer 1892a and 1892b). With 

 these stains available there are very few 

 small invertebrates or invertebrate larvae 

 which cannot be prepared. 



Larger Invertebrate Specimens, 

 Larger specimens are better stained by the 

 direct process: that is, exposed for a con- 

 siderable length of time to a very weak 

 solution of stain and subsequently not dif- 

 ferentiated. Tills process is described in 

 considerable detail for the fiver fluke in 

 Chapter 20; the directions there given ap- 

 ply equally to earthworms, leeches, or 

 medium-sized polychaetae. 



Vertebrate Embryos. These seem to 

 stain more satisfactorily in hematoxyhn 

 than in carmine solutions, the author's 

 preference being for the formula of Carazzi 

 (Chapter 20, DS 11.122 Carazzi 1911). 

 This formula is not very well known but 

 may be used whenever the solution of 

 Delafield is recommended. Detailed in- 

 structions for the use of this stain on a 

 chicken embryo are given in Chapter 20. 

 People who wish to produce a startling, 



