254 
Ellis . — The Life-history of Bacillus hirtus. 
of motion which are to be observed in this genus. It seems doubtful that 
the cilia can account for all the different varieties of motion. Recently it 
has been shown (8) that very probably the motility of the diatoms is due to 
the evolution of oxygen gas, which sufficiently accounts for the vagaries of 
these individuals. It is possible that the motion of any particular microbe 
is the resultant of these two forces, the vital activity of the cilia, and the 
movement caused by the evolution of gas. It would be interesting to com- 
pare the movements of a form of bacteria in which gas is known to be 
evolved, e. g. Bacillus coli-communis , with the movements of a non-gas- 
producing form, in order to ascertain whether there would be any differences 
due to the evolution of gas affecting the nature of the motility. 
When twenty-four hours old cultures are examined, there is never a 
lack of active motion in normally developed growths. This age is usually 
best suited for cilia preparations. In Fig. 46 is shown one made from a 
culture of this age. I11 a three days old culture, unless spore-formation is 
very far advanced, which, as stated above, is not usually the case, the 
majority of the individuals are still motile. Usually at this stage a small 
number have either proceeded too far in the formation of spores or else, as 
is seen in the reduced intensity with which they take up stains, are either 
dead or in an extremely unhealthy condition. In both these cases there is 
no motility. In individuals, however, in which no spores are being formed 
or in which spore-formation is not far advanced, the motility is as great as in 
younger cultures. In the further growth of the culture the motility ceases 
owing to the extensive formation of spores, but even in 10-1 5 days old 
cultures there can always be seen a few motile individuals. As in 
reinoculation these asporogenous individuals divide and multiply, it is advis- 
able before reinoculation to heat the material sufficiently to kill these forms 
but not the spores, if it be desired to obtain an abundance of spores. So 
far as motility of bacteria in general is concerned, as previously stated I do 
not think that a single cylindrical or round form of bacteria exists which 
cannot be made motile by suitable cultivation. In all forms which I have 
examined persistency in continual inoculation has invariably produced this 
result, so that motility in bacteria is a question of degree and not a question 
as to its existence or non-existence. It is important to emphasize this 
point, because the two latest and best classifications, viz. by Fischer ( 5 ) and 
by Migula ( 11 ), adopt the presence or absence of motility as a mark of 
ordinal importance, whereas, as a matter of fact, it is not even a specific 
value. 
Contents of the Cell. 
To secure the material in the most favourable condition, the material 
must be fixed in a drop of 5o°/ o Formol for about three or four minutes. 
Then the stain (preferably Fuchsin) is added by means of a platinum-loop, 
