Walter Stiles 
4 
branes are impermeable to the substance produced. There may, of 
course, be a number of different substances present in the cell capable 
of forming non-diffusible compounds with methylene blue or other 
dyes, but the only substance in addition to tannin which has so 
far been recognised as capable of this appears to be phloroglucinol 
(Waage, 1890; Klemm, 1892). It might also be possible to account 
for the accumulation of the dye in the cell sap by adsorption. If this 
were so, one would expect the highly colloidal protoplasm to play 
a greater part in adsorbing the dye than the less highly colloidal cell 
sap. Nevertheless in the case of methylene blue no appreciable 
coloration of the protoplasm by the dye is observable, but on the 
other hand, rosolic acid was observed to enter the protoplasm so that 
the latter became visibly coloured, whereas no accumulation of the 
dye in the vacuole was observed. All the other dyes recorded above 
as entering the cell both accumulate in the vacuole and stain the 
protoplasm. How such “vital staining,” that is, the staining of 
living cells by the accumulation of dye (“ intra-vitam stain ”) in the 
cell, takes place, will be considered in a later chapter. 
With nigrosin, aniline blue, methyl blue, marine blue, aniline grey, 
eosin and congo-red, no visible intake of the dye into living cells 
could be observed, although penetration may be rapid enough into 
dead cells. Even after three days’ immersion in a 1 per cent, solution 
of aniline blue or a 0*5 per cent, solution of nigrosin no coloration was 
observable of the cell sap of (?) root hairs of Trianea bogotensis 
immersed in these very densely coloured solutions, and the cells were 
uninjured. Similarly indigo-carmine when presented to Spirogyra 
setiformis and Trianea in 0-7 per cent, solution, was not absorbed 
even after four days; even the cell walls were not stained and the 
cells remained alive. 
Apparently none of the dyes examined by Pfeffer are absorbed 
either by the nucleus or chromatophores if the cell remains alive. 
Only after the death of the cell can the nucleus become stained, 
and methylene blue, for example, can then be absorbed by the nu¬ 
cleus. But Campbell (1888) working in Pfeffer’s laboratory showed 
a little later that the nucleus of living cells can be stained by some 
dyes, as for example, dahlia and mauvein. Other cases have since 
been recorded by Lauterborn (1893) and Palla (1893), for example. 
This possibility was fully recognised by Pfeffer, who pointed out that 
indigo-carmine had been shown to stain the nuclei of living kidney 
cells (Heidenhain, 1874), while different kinds of cells may vary in 
regard to the staining of bodies contained in them. Thus the micro- 
