The purpose of using a stain in microscopy, is firstly to render transparent objects more opaque and secondly, to find out something about their chemical composition. The affinity for a stain is largely dependant on the composition of the various parts of the cell and a single cell will differentially stain by virtue of its heterogeneous composition. For example, the protoplasts of the Zebrina guard cells were stained brown and the starch grains black by iodine solution. The cell wall became a yellowish colour, but was not very efficiently differentiated from the cytoplasm. It would however have been possible to stain the cell wall with another reagent which had a specific affinity for cellulose. Thus whilst it is possible to differentiate some of the cell components by using a single stain or reagent, this can be done more effectively by using two (or more) stains, each more or less specific for a certain component. The two stains may be applied separately or may be combined in a single solution. Fabil stain consists of a mixture of dyes, incorporated in a mounting medium. The plant material, either fresh or preserved, is mounted directly in Fabil. It may be examined immediately, but the staining will be found to be better after about 5 to 10 minutes immersion, and continues to improve for some time. The main colour reactions are:

Technique 10: Making and using FABIL stain

FABIL is used extensively in our laboratories, for staining freehand sections. It is necessary to make up three stock solutions first before mixing these proportionally to make the stain itself. Please note: FABIL ripens and improves with age. It is also advisable to filter the stain to remove aggregated precipitate from time to time.

Stock Solutions.

The stain is made up by mixing the stock solutions in the following proportions:

A=4: B=6: C=5

Allow the mixture to stand overnight and filter the next day. The stain ripens and improves with age. Periodic filtering is highly recommended. 

LACTOPHENOL (take care not to get any of this on your clothes or skin. Wash immediately under cold running water) 

Dissolve phenol in H2O without heat. Then add glycerin and lactic acid.