122 SPECIFIC EXAMPLES OF SLIDE-MAKING 



of tissue studied and is greatly dependent on temperature. If the solutions are 

 heated to 50° C, with the understanding that this will cause a swelling of the 

 section and a general obscuring of the finer details, the period may be short- 

 ened to as little as 10 minutes. The finest stains, however, are those secured by 

 leaving the sections in the mordant solution at room temperatures overnight. 

 On removal from the mordant solution, the sections should be rinsed very 

 briefly in distilled water; the purpose of the rinse is to remove the surplus 

 mordant from the surface of the slide without extracting it from the tissues. 

 Then the slides are placed in the hematoxylin solution where they should re- 

 main for approximately the same period as they have been in the mordant; 

 the length of time is not important, though from 3 to 24 hours is the custom- 

 ary period. Sections may be removed from time to time from the staining so- 

 lution and examined with the naked eye. Successful preparations show the 

 sections to have been blackened completely, although a slight bluish tinge in 

 the black is permissible. If they have not become blackened completely in 

 24 hours, it is necessary only to place them, after a brief rinse, in the mordant 

 solution and leave them there for another 24 hours before returning them 

 to the stain. 



If, however, the sections are sufficiently blackened on removal from the stain- 

 ing solution, they may be differentiated; that is, the hematoxylin stain ex- 

 tracted from all portions of the sections except the chromosomes, which are to 

 be studied. This is done customarily with the same solution in which they were 

 mordanted, though, of course, a fresh solution or a stronger solution may be 

 employed if desired. Differentiation at the commencement of the process goes 

 relatively slowly, so that all the slides, which are carried in a glass rack, may 

 be removed and placed in the 2.5 per cent iron alum without any very great 

 care. The actual time in which differentiation takes place cannot be forecast 

 since it depends on a large number of uncontrollable factors; it is never less 

 than five minutes nor is it very often more than a few hours. Sections, there- 

 fore, should be withdrawn from the iron alum every four or five minutes and 

 examined briefly under the low power of a microscope. It is a matter of great 

 convenience for the controlling of differentiation of chromosomes in this type 

 of preparation if an ordinary student microscope (of the type customarily used 

 in laboratory) can be lifted with a glass plate over the stage, so that one can, 

 without fear of damage to the instrument, place a slide, wet with iron alum, 

 on the surface of the stage for examination. No more common accident takes 

 place than the placing of the slide upside down on the surface of the stage 

 with the subsequent loss of all the sections. This will be avoided readily if the 

 worker will make it a matter of routine, as he lifts the slide from the mordant, 



