Ellis . — The Life-history of Bacillus hirtus. 
245 
Growth on Dextrose-Agar. 
I have examined in detail the growth of this organism on Dextrose- 
Agar, from spore-germination to spore-formation in the next generation, in 
order to obtain a general idea of its life-history. The Dextrose-Agar was 
made up of the following materials : Agar, 1 -6 grams ; Dextrose, i-o gram ; 
Na, 0-2 gram; Lemco, i-8 grams; Peptone (Witte), 1-2 grams; Water, 
100 c.c. In all cases growth commenced from the spore. This was effected 
by heating the spore-material for two minutes in boiling water, which thus 
killed off the vegetative cells but would not appreciably diminish the 
germinating power of the spores. The spore-material was placed in a drop 
of sterile water, contained in a small sterile test-tube. The latter was then 
immersed in the boiling water. After heating the spores were sown over 
the surface of the nutrient Agar and then incubated at 32°C. 
Germination . — The details of germination are given above. 
After fifteen hours. — The appearance of the culture after fifteen hours 
varies considerably. Sometimes rapid growth has taken place, which is marked 
by the appearance of a light grey, somewhat transparent layer. Sometimes, 
however, the growth has been slow, and it is only by holding the culture up 
to the light that it is seen that growth has taken place ; a filmy covering is 
seen which is very transparent. At this stage almost all the individuals are 
either i-celled (Fig. 16) or 2-celled (Fig. 17) and very motile. The mo- 
tility is of five kinds. 
1. A forward movement accompanied by a violent wriggling of the 
whole body. 
2. A forward movement accompanied by a fairly rapid oscillation in 
which the centre of the cell is the fulcrum. 
3. Rotation. 
4. A forward followed by a backward movement along the same 
direction, or else a sharp turn in another direction. 
5. Violent trembling of the whole body unaccompanied by a forward 
movement. 
In fact all the varieties of motion which can be observed in a member 
of the genus Bacillus can be seen in a fifteen hours old culture of this 
species, provided that growth has been favourable. After twenty-four hours 
no great change has taken place in the appearance of the individuals as 
seen under the microscope, although there is usually a far thicker growth 
on the surface of the Agar. This takes the form of a somewhat light grey 
layer, the commonest of all colours on Agar cultures. The individuals were 
examined by means of the stains, Iodine, Methylene-blue, Bismarck-brown, 
and Fuchsin, all of which serve their purpose very well. The intimate 
structure of the cell is discussed in the section dealing with the cell-contents. 
In a tzvo days old culture the light grey covering is continued so as to 
form a pellicle on the surface of the condensed water. This formation is 
