TEXT-BOOK OF BACTERIOLOGY. 39 



First we have a violet dye, the gentian-violet, which is distin- 

 guished by particularly strong staining action. It is not a pure 

 chemical substance, but probably owes its peculiar jjowers to for- 

 eign admixtures. Another somewhat similar violet is the methyl- 

 violet; and there is a blue dye, methyl-blue. For red, we have 

 fuchsin, or rubin; for brown, the Bismarck-brown or vesuvin. All 

 these anilin colors have the common property of containing a 

 proper staining ingredient of a basic character; thej"- are the basic 

 anilin dyes. To them belongs by far the most important place in 

 bacterial investigations, yet some of the acid anilin dyes are also 

 used, especially eosin and acid fuchsin. 



In addition to these bodies, we also employ a staining agent 

 which comes from the vegetable kingdom. This is hcematoxylon 

 prepared from Campeachj' wood (logwood), and lastly an animal 

 product, carmine, obtained from the C9.rdinal insect. There exist 

 also, as before mentioned, a great number of other stains, more or 

 less similar to the above, which were formerly in use, but of far 

 less importance than those just named. 



In the great majority of cases, the colors mentioned will be 

 found fully sufficient, and there is not for the present anj^ pressing 

 need to enlarge the list. 



In what does the peculiar action of these stains consist, and 

 what is it that makes them indispensable for our purposes ? Ex- 

 amine a section from the liver of a healthy rabbit. Transfer it 

 from alcohol to a saucer containing a diluted solution of an anilin 

 violet color. After it has remained a short time — about two 

 minutes — take it out, remove the superfluous staining matter by 

 washing in distilled water acidulated with a few drops of acetic 

 acid, place the section on a slide, lay a thin cover-glass over it, and 

 examine it with a medium power. 



If, in order to get the color picture separated as much as possi- 

 ble from the structure-picture — i.e., to see the peculiar action of the 

 stains — use no diaphragm, but with the full illuminating power of 

 the Abbe; the texture of the tissue will be found, on the whole, less 

 distinct than formerly with the uncolored object and without the 

 Abbe. 



The outlines of the cells are not sharp, the smaller vessels are 

 almost imperceptible, the connective tissue shows only slight traces 

 of stain, and the more delicate parts of the structure are quite un- 

 recognizable. But something strikes the ej^e at once, and that is 

 the strong distinctive staining of the cell nuclei, which, at the first 

 glance, enables us to distinguish them from surrounding struc- 

 tures. Hardly anything but the nuclei is seen, and while it was 



