NEU1RAL RED IN HISTOLOGY AND BACTERIOLOGY. 
629 
In general the fluorescent and brown color indicate an alka¬ 
line reaction ; the red the presence of an acid or a neutral con¬ 
dition. Between these two groups some intermediate conditions 
may be found, as for instance, when the media may contain a 
greatei or less amount of grape sugar, certain of the bacteria 
may give, at first, an acid followed by an alkaline reaction ; or 
an apparently opposite condition may be shown as in one case 
of the bacillus coli communis grown in a fermentation tube of 
glucose. There soon appeared the fluorescence but the litmus 
paper demonstrated an acid reaction, later the fluorescence disap¬ 
peared and the characteristic red (acid) color returned. 
The change of the red to the fluorescent and brown color is, 
m general, caused by the alkalinity; but it will also be remem¬ 
bered that alcohol turns the red to a brown, and that with the 
proper conditions as to the presence of grape sugar and reaction 
of the bacteria, some alcoholic fermentation may be set up, 
which in the above mentioned case of the bacillus coli in 
glucose, may account for the unexpected fluorescence with 
an acid reaction and likewise be of some service as a test for 
alcohol. 
When fluorescence does occur in the fermentation tube it is 
usually more distinctly shown in the closed tube than in the 
bulb. The greater volume of the fluid in the latter is perhaps 
the explanation for this. 
Rather an unusual amount of crystallization developed in the 
agar and gelatin media. While this phenomena is not uncom¬ 
mon in these media as ordinarily used, the addition of the red 
seemed to develop the crystals quite constantly and in unusual 
quantities. They were quite inconstant as to color, size and 
form, m the different species and the variations met with in 
these respects, although perhaps of no use diagnostically, seemed, 
nevertheless, worthy of mention. 
’94 Ehrlich. Ueber Neutralroth, Zeit. f wiss. Mikros. XI.— 250. [Abstract.] Aus 
<lem Bencht “ Uber dem Ehrlichschen Vortrag im Verein fiir Innere Medicin ” zu Berlin 
i8 / I2 > 3 - Allgem. Med. Centralzeitg. 1894. No. 2, p. 20. 
’ 94 - Galeotti Gino. Recerche sulla colorabilita delle cellule viventi. 
Zeit. f wiss. Mikros. XI. 172-207. 
