REAGENTS 33 



showed scarcely any shrinking of cell contents, the filaments were not 

 breaking up, and even the color had scarcely faded. 



A 6 per cent solution will fix one-fourth its volume of material. 

 With material like filamentous algae or leafy liverworts, a 10 per cent 

 solution will fix all one can put into the bottle without crowding. 



For class use, material should be washed in water for several 

 minutes, because the fumes are irritating to the eyes and mucous 

 membranes. 



For a study of chondriosomes or the origin of vacuoles, the follow- 

 ing combination is satisfactory: 



Bensley's formula. — 



1. Formalin (neutral) 10.0 c.c. 



2. Dichromate of potash 2 . 5 g. 



3. Corrosive sublimate 5 . g. 



4. Water 90.0 c.c. 



Make the solution 2, 3, 4, and then add the neutral formalin. Fix 

 about 24 hours. Wash in water, but use the iodine — necessary on 

 account of the corrosive sublimate — just before staining sections on 

 the slide. 



Yamanouchi's formula. — 



Formalin (neutral) 10 c.c. 



Water 100 c.c. 



This simpler formula brings out the chondriosomes very clearly. 

 Fix overnight or even 24 hours. A thorough washing is easy and 

 staining is brilliant, especially with Haidenhains iron-alum haema- 

 toxylin. 



GENERAL mNTS ON FIXING 



Since it is desirable that a fixing agent penetrate quickly to ah parts 

 of an object, the material should be in small pieces. 



The best fixing agents do their best work near the surface of the 

 piece. Of course, filamentous algae and fungi, and delicate objects like 

 fern prothallia and root-tips, are simply thrown into the fixing agent. 

 Alcohol, formahn alcohol, or formalin alone may penetrate j-inch 

 cubes; but the chromic-acid series, which gives the best results in 

 cytological work, penetrates so poorly that cells more than jV i^^ch 

 from the surface are not likely to be well fixed. Most objects should be 

 trimmed with a razor so that no part shall be more than j\ inch from 



