Freehand Sections 89 



and Delafield's haematoxylin, and mounted in balsam, the entire 

 time being less than 30 minutes. This is an extreme case, and 

 nothing is gained, except time, and the saving of time is apparent 

 rather than real, for the histologist always has something to do while 

 the sections are in the stain. 



Preserved Material. If sections are to be cut from material 

 preserved in formalin, the piece should be washed in water, since 

 the odor is annoying and the fumes are injurious to the eyes. 



The sections are placed in the stain from water. Sections from 

 alcoholic material are transferred directly to the stain. If the 

 material is in a mixture of alcohol and glycerin, the sections should 

 be washed in water or 50 per cent alcohol until the glycerin has been 

 removed before transferring to the stain. 



Some material cuts well when fresh, but cuts with difficulty when 

 preserved. On the other hand, some material cuts well when pre- 

 served, but hardly at all when fresh. Some material which is too soft 

 to cut when fresh can be cut with ease after it has been in formalin 

 alcohol for a week or more. 



Very hard material, like oak, hickory, maple, etc., should be 

 boiled in water and treated with hydrofluoric acid before any section- 

 ing is attempted. Cut the material into blocks suitable for sections 

 and boil in water for several minutes; then transfer to cold water and, 

 after several minutes, repeat the boiling. The alternate boiling and 

 cooling, which should be repeated several times, drives out the air. 

 Transfer to equal parts of commercial hydrofluoric acid and water. 

 From 1 to 3 weeks will be enough for most woods. Some oaks, ebony, 

 apple, etc., may require a longer time and the acid may be used pure. 

 Wash thoroughly in water for a day or two. Then leave in equal 

 parts of 30 per cent alcohol and glycerin for several days before 

 cutting. Material may be left indefinitely in the mixture of 

 glycerin and alcohol. 



OBJECTS MOUNTED WITHOUT SECTIONING 



Fern Prothallia, mounted without sectioning, make very useful 

 preparations. Select desirable stages and fix in chromo-acetic acid 

 for 10 to 24 hours; \vash in water for 3 or 4 hours, changing the water 

 frequently; stain in Delafield's haematoxylin for 5 to 30 minutes; 



