654 
Notes. 
gelatine by the method described in my Fourth Report to the Royal 
Society Water-research Committee 1 , and so arranging matters that the 
gelatine-drop, &c. forms a plate-culture, the floor of which is the thin 
cover-slip. In fact, if we suppose a modified Petri-dish with the glass 
floor so thin that the whole thickness of the gelatine film can be optically 
pierced by a one-twelfth immersion, the essential conditions are obtained. 
When the colonies become visible to the unaided eye, it is easy to 
inoculate a tube and test the purity of the culture, &c., by the ordinary 
methods. 
In other cases, I utilized the method of preparing Klatschpraparate. 
A sterile cover-slip is held by sterile forceps and laid flat on a growing 
colony, a thin film of nutrient gelatine having been distributed over 
the contact side of the cover-slip : this is then lifted and used as if it were 
a hanging-drop preparation. The adherent Bacilli, fixed in situ on the 
film of gelatine, can then carry on their growth, &c., under observation. 
It usually happens that when a rodlet, fixed in solid gelatine, grows 
to twice its length and then divides, the two daughter-cells slip one 
over the other as if the elasticity of the gelatine made itself effective on 
the free distal ends, and this phenomenon is repeated, so that when say 
a dozen or twenty divisions have occurred, we have a group of rods 
irregularly side by side in a spindle-shaped micro-colony. It is in this 
way that the frequent occurrence of ‘ whetstone-shaped ' and ‘ oval * sub- 
merged colonies is to be explained. Subsequently, as the gelatine is 
softened around, these may gradually round off to a spherical shape. 
Another proof that the elasticity of the gelatine comes into play is 
afforded by such observations as the following. A Micrococcus or 
Bacillus having divided many hundreds of times, forms a perfectly 
spherical colony. The gelatine then softens at one point on the 
periphery of the submerged sphere, whether by local increase of 
enzyme or otherwise does not matter, and a rounded protuberance of 
the colony at once forces its way into the softer gelatine, converting 
the whole colony into a pyriform shape. As this occurs, all the 
diameters of the rounded part of the pear — i.e. the previous sphere — 
perceptibly diminish. In other words, the elastic pressure of the 
gelatine forces the colony to bulge into the yielding gelatine. Later 
on other local protuberances may occur in the same way, and the 
rapidly enlarging colony then assumes moruloid or lobed shapes, such 
as are common in submerged colonies. 
1 Proc. R. Soc., vol. lviii. pp. 12 and 13. 
