238 Ellis . — The Life-history of Bacillus kirtas . 
organism like Bacillus subtilis must have appeared, I have no doubt, under 
a dozen different names. 
In all cases, growth on gelatine-plates begins to be apparent by the 
appearance of minute greyish-white specks, both on the surface of the 
gelatine as well as beneath the surface. The latter colonies do not proceed 
much further. The superficial colonies, however, are round, have sharp 
contours, and each colony appears denser in the middle than at the sides, 
because owing to abundant growth the middle part is raised more above 
the surface than is the peripheral growth. It often results in the appear- 
ance of a ‘ nucleus ’ at the centre of a colony. Again, as a peptonizing 
ferment is present, the appearance of the edge of the colony begins to alter, 
and as described by Henrici, the beginning of liquefaction is the cause of 
the various strata which the colonies exhibit, the one furthest from the 
centre being of course the most transparent. Again, the colonies have at 
first sharply defined edges, but later become irregular and often exhibit 
* blitzahnliche Auswiichse/ It must not be expected that these outgrowths 
invariably occur, and as a matter of fact in about 5 °% °f the gelatine-plates 
they are absent. It depends on the constitution, density, dryness, &c., of 
the gelatine whether they occur or not. Again it must be borne in mind 
that many other Bacteria possess the same characteristics. Another point 
which should be noticed is that the relation between time and the size 
of the colonies is by no means constant. The growth on Henrici’s gelatine- 
plates was extremely rapid : in all those which I made I did not obtain 
a quarter of the growth mentioned by him, though ultimately as large and 
larger growth was obtained when the colonies were not too crowded. The 
following results show the relation between size and time in a few instances. 
They were not all made at the same time of year, hence as the tempera- 
tures were necessarily different, another factor is introduced. It suffices 
to show that for any given form no constancy in this respect can be 
expected. 
I. Minute specks after eight days, which after fourteen days showed 
a diameter of i*5-2-o mm. 
II. Minute grey colonies after three days, which became very thick 
and granulated and completely liquefied the gelatine in 
thirteen days. 
III. Minute grey colonies after two days. Gelatine completely 
liquefied after nine days. In this experiment the plates were 
placed on top of an incubator and were therefore 
slightly warmer than the surrounding atmosphere. 
Other experiments, not recorded, showed the same variations in the growth 
and liquefaction of the gelatine. 
The following are not to be depended upon, in diagnosing a species by 
means of gelatine-plates. 
