Envelopes for Filing Microscopic Slides

The writers discuss a series of investigations as to the behavior of certain fluorescein dyes (eosin, erythrosin, phloxine, and rose bengal) in staining bacteria in dried films of soil. These dyes are ordinarily purchased in the form of di-sodium salts and are indifferent staining agents for the purpose named. If there be added to the dye solution a small amount (0.001 to 0.1%) of a mineral salt of calcium, aluminium, magnesium or lead, the intensity of staining is greatly increased. The effect of such addition is to convert the dye partly into a salt of the metal added, which in nearly every instance is relatively insoluble and is in every case less soluble than the di-sodium salt. It is shown that practically identical results can be obtained if the staining be performed with a suspension of the calcium, aluminium or lead salt of one of these dyes, altho very little of the dye goes into solution.

Theories to account for the phenomenon are discussed, including in particular the solution and adsorption theories of staining. The evidence seems to favor the former, altho not entirely disproving the latter.