246 Ellis . — The Life-history of Bacillus hirhis. 
never wanting. Microscopically the presentation is almost the same as in 
a one-day-old culture, except that there is a slight increase in the number of 
2-celled as opposed to 1 -celled individuals. This is to be expected in an 
older culture for, as stated above, there is present a larger amount of 
excreted matter which cannot but be unfavourable to growth, and in 
addition the amount of available food which can be drawn upon must be far 
less than it was twenty-four hours previously. In most cultures of this age 
there is no sign of spores, though sometimes cultures pass through the stages of 
growth very quickly and some individuals have begun to form spores even 
after two days. The motility is unabated, and as is seen in Fig. 18 the 
cilia have the peritrich arrangement characteristic of the genus Bacillus . 
There is no appearance of degeneration in the cells, as the cytoplasm 
always presents the same dense appearance in all the cells, when stained 
with the usual colour-reagents. I find Methylene-blue to be the best for 
this purpose, as when a dead cell is stained with it, not only is its cytoplasm 
very much less densely stained than that of a cell which was alive when 
treated with Methylene-blue, but the colour alters appreciably, changing to 
a more purple hue. At this stage the number of dead cells is extremely 
small. In a three days old culture , a great change has usually taken place. 
If the culture be normal, almost all the individuals are beginning to form 
spores, and very many of these spores have the glistening appearance 
peculiar to mature or nearly mature spores. The motility is unchanged in 
those individuals in which spore-formation has not taken place, and very 
often the individuals showing spores are also motile. Usually, however, the 
latter have come to rest indicating that a loss of ciliation has occurred due 
to the withdrawal of cytoplasm, in order to supply the spore, but motility 
remains in those individuals in which the demands of the spore have not 
exhausted the cytoplasm of the cell, for it is evident that an independent 
thread of cytoplasm like a cilium cannot remain functional apart from the 
cytoplasm of the interior of the cell, and if the latter be used up to form a 
spore, the detachment and consequent falling off of the cilia must inevitably 
take place. I have demonstrated in a former paper ( 3 ) the manner in 
which the cilia penetrate the cell-walls and establish continuity with the 
cytoplasm inside the cell. In Fig. 19 is shown a case in which spore-forma- 
tion has not completely exhausted the cytoplasm, and these must be the 
individuals which, whilst forming spores, do not lose for the present their 
motility. As regards the non-sporing individuals, their structure does not 
differ from that of individuals taken from one-day and two-day-old cultures. 
At this stage a certain number of individuals have been cut off in the 
struggle for existence, and when stained with Methylene-blue, or any of the 
other stains, indicate their condition by the weakness of the colouring, 
and with Methylene-blue, as was mentioned above, by a change in colour 
as well. 
