Notes. 
655 
If the direction of least pressure on a submerged spherical colony 
of the above description happens to be at right angles to the free 
surface of the gelatine-film, then the colony bursts to the exterior and 
emerges as it were like a fountain, oozing out its Bacilli or Cocci, &c., 
in the form of a button-like drop, or a flat cake, film, &c. according to 
circumstances. In these cases the dark submerged ‘ manubrium ’ of 
the colony shows long after emergence the point in gelatine where the 
Bacilli burst through. 
If, on the other hand, the still submerged spherical colony begins to 
liquefy the gelatine equally all round its periphery, a beautiful play of 
chemotaxis comes in : the superficial Bacilli arrange themselves at 
right angles to the periphery, in the zone of liquefied gelatine, and 
form a radiating fringe. In some cases this may be brought about by 
softening of the gelatine by a slight rise of temperature, and possibly 
by other agencies than the direct liquefying power of the Bacilli. 
Turning now to emerged colonies. It is pretty clear that the flow 
over the free surface of the gelatine may be affected by several factors, 
and especially by the degree of moisture. If a damp film exists, or if 
the Bacillus can slightly liquefy, the free spreading of the colony is 
favoured much more than when the gelatine is relatively dryer or the 
Bacillus weak, and it is obvious how this may be profoundly affected 
by tardy emergence, differences in hygroscopic properties of the 
gelatine-film, dry or moist atmosphere, temperature, &c. Several 
cases are given where colonies of one and the same form behave in 
this respect so differently on emergence, that they might be taken for 
different species, and would probably be so described by bacteriologists 
unacquainted with these phenomena. 
That the liquefying power of Bacteria varies is well known, and 
I have been able to show that with comparative plate-cultures of one 
and the same form the rapidity of liquefaction, like the rate of growth, 
can be affected by exposure to light and other agents, and in these 
cases the appearance of the resulting colonies may be so different that 
no one would suppose them to belong to the same species. 
In pursuance of the subject, I have made a large number of cultures 
to see if exposure to light alone will so affect the organism that its 
after-behaviour is modified. Several species have been exposed in 
tubes of broth or of water to sunshine, with control tubes shaded from 
the light. The usual effects — death of Bacilli in the light, and re- 
tarded growth of those which survive — were confirmed, but it has not 
