142 
by pectin compounds, which thus reveal their acid function. They do 
not stain callose or cellulose. The following compound s are noteworthy: 
Azo group Yesuvin brown, chrysoidin; diphenyl-methane group , aura- 
mine ; triphenylmethane group , the Victoria blues, bleu de nuit, fuch- 
sine, Paris violet, Hofman’s violet, etc., all the stains of the oxazine 
group , naphthaline blue, Nile blue; thionine group , methyl blue; euhro- 
dine group , neutral red; safranine group , neutral blue, pheno-safranine 
extra safranine, rosaline, Magdala red. The affinity of these substances 
for pectin compounds is very dissimilar. It is also feeble, for the pres¬ 
ence of an excess of acid or of glycerine removes the stain from the tis¬ 
sues more or less readily. 
The second category, formed of alkaline salts, contains a great num¬ 
ber of substances which never stain pectin compounds. Many, how¬ 
ever, are fixed by cellulose and callose, and thus show the basic nature 
of these latter, a nature already known and used for a long time, so far 
as concerns cellulose. In this category only two groups are of interest 
the azo group and the triphenylmethane group. The azo group, exclu¬ 
sive of chryso'idine and Yesuvin brown, is composed principally of alka¬ 
line salts. In this group we distinguish three important types. The 
first includes the various stains which contain the azo grouping once, 
e. g ., xylidine ponceau, aniline ponceau, toluidine ponceau, naphthoru- 
bin, etc., as well as various tropeolines of a slightly different composi. 
tion. These substances stain protoplasm yellow, but they have no 
action on cellulose and callose. The second type is formed of sub¬ 
stances containing the azo grouping twice, e. g ., orseille red, orseilline 
BB, azorubine, naphthol black, the croceines, etc. These substances 
stain cellulose in a neutral or slightly acid bath, but have no effect on 
callose. The third type contains the stains of the benzidine series, e. g. 
Congo red, Congo GR, Congo brilliant G, Corinthian Congo, extra 
Bordeaux, delta purpurine G, which result from the action of sulpho- 
nated naphthol compounds upon benzidine; azo blue, Corinthian Congo 
B, the benzo purpurines and the rosazurines, in which toluidine is sub¬ 
stituted for benzidine; azo violet, the benzo azurines and heliotrope, 
where dianisidine is substituted for benzidine. These colors, ordi¬ 
narily precipitated by acids, stain cellulose directly in a neutral or, 
better, a slightly alkaline bath. 
The triphenylmethane group does not offer as distinct relations be¬ 
tween staining capacity and chemical composition. We first distin¬ 
guish a large number of bodies formed by chlorhydrates, sulphates, 
etc., which stain pectin compounds directly. Then a series of alkaline 
salts which may be divided into three groups. The first group in¬ 
cludes acid fuchsine, acid violet, Bayer’s blue, the alkaline blues, etc., 
which result from the respective action of sulphuric acid on fuchsine, 
Paris violet 6B, diphenylamine blue, and analine blue. These sub¬ 
stances do not stain cellulose, but certain of them stain callose, e. g ., 
the soluble blues, and notably Bayer’s blues. The staining is energetic 
