250 Ellis— The Life-history of Bacillus hirtus. 
the whole mass suddenly separated into its component parts, and each 
individual began a separate existence. This naturally caused them to 
disappear from the microscope-field. From the data here supplied, the 
time necessary for a single complete division from beginning to end was 
3 * .fi° = 25 minutes. 
7 
If we bear in mind how short a time it takes for an Agar surface 
to be completely covered with a thick growth when it has only been 
inoculated at a single point, it must often happen that a complete division 
takes place in less time even than twenty-five minutes. 
Development of Spores. 
To observe the formation of spores, material was taken from a three 
days old culture, in which, as a general rule, a number of spores of all ages 
is seen in the microscope-field, and there will usually be a large number of 
individuals showing the early stages of development. Meyer’s stain (10) 
given for nuclear coloration does very well for the first stages of spore- 
development, but it is necessary to modify the method, so far as the 
quantity of stain to be used is concerned. The method which I employed 
consists in fixing the material for three or four minutes in a drop of Formol, 
then staining by adding to the Formol a few loopfuls of a solution made up 
as follows - 
2 c.c. ale. sat. solution Fuchsin. 
10 c.c. abs. ale. 
10 c.c. H 2 0 . 
Sometimes it will be found advisable to dilute the Formol with water. 
With regard to the number of loopfuls of the stain which will be required, 
that must be tested in each individual case : sometimes good results are 
obtained by using four or five loopfuls to the drop, and examining after 
four minutes. At other times, especially when the drop is comparatively 
small, we can use less of the stain, and examine after a longer interval. 
Again, results quite as good can be obtained by using other stains, 
e. g. Methylene-blue. A good stain can be obtained by mixing 1 c.c. 
of a saturated alcoholic solution of Methylene-blue and 40 c.c. of water. 
Care must be taken that the drop containing the material does not 
dry up, otherwise accurate observation of young spores is impossible. 
The first stage in the development is seen in the formation of a clear 
oval area in the interior of the cell (Fig. 35). This space is of the 
same size as the mature spore, and represents, as it were, the site that 
will be occupied by it. This space is clearly marked off from the 
surrounding cytoplasm, but this depth of staining does not differentiate 
the cytoplasm from the wall. In one instance I observed 12-15 cells 
attached together, all of which were at this stage of development. In each 
