288 Trow. — Observations on the Biology and 
For purposes of comparison other methods of fixing and 
staining were used. Mercuric chloride solutions, platinic 
chloride solutions, and acetic alcohol were used for fixing, 
in addition to those already mentioned. The best results 
were obtained with Flemming’s solution, chromacetic acid, 
and Hermann’s solution, and of these the first two were 
somewhat better on the whole than the third. Flemming’s 
solution preserved the details of the protoplasm better than 
the chromacetic acid, and the nuclei could be followed at all 
stages with almost equal facility. The stains chiefly used 
were gentian violet, haematoxylin, and safranin. Gentian 
violet gave excellent results. Safranin proved useless although 
much time was expended over it. With gentian violet or 
iron-alum haematoxylin it is possible to decolourize the cyto- 
plasm and yet leave the whole nucleus either deep violet or 
black. The counting of the nuclei is very easy in such cases. 
By further differentiation the detailed structure of the nucleus 
is disclosed. With safranin diffuse staining was alone possible. 
After many experiments with two kinds of safranin (Griibler’s), 
using the stain alone and in combination, no single section 
was found with good differentiation. 
It is probable that equally good results would have been 
obtained with the material fixed in chromacetic acid, but 
time was not available for the detailed study of a third series 
of sections. It is noteworthy that although Flemming’s solu- 
tion kills the protoplasm instantly, and blackening is observ- 
able in a minute or two, very poor staining results were 
obtained when the time of action was limited to an hour. 
As Flemming has pointed out the special action of the chromic 
acid is a slow one. 
Of the two series of sections fully examined, one was of 
material obtained from impure cultures in which Bacteria 
were present, the other was of material from absolutely pure 
and very fine cultures. These series were fixed and stained 
in different ways, but the results were always concordant. 
The pure cultures were of advantage, however, with respect 
to one point, as will be seen later. The illustrations, with 
