6 5 6 
Notes. 
as yet been possible to obtain a distinct varietal form definitely due to 
the modifying action of the light alone from these tubes. On growing 
colonies in the dark, in normal gelatine, the Bacilli retarded by the 
light- action slowly recover their usual characters after a time. Even 
after numerous transferences from light-tube to light-tube, and dark- 
tube to dark-tube, day after day, the same recovery occurs, and the 
colonies are not affected in any permanent way. 
While actually growing in gelatine, on the other hand, very slight 
exposures affect the appearance of the colonies, and if the effects of 
varying temperatures (within limits in no way fatal to the plants) 
are superposed on those of light, some marked changes in shape, rate 
of growth, and even pigmentation may be induced. 
Much research will be necessary, however, before the problems here 
raised are settled. 
Growth is very easily affected by much slighter changes of con- 
dition than is usually accepted, and my experiments convince me that 
plate-cultures ‘ at ordinary temperatures ’ — or ‘ at the temperature of 
the room 5 {Zimmer temper atur ) — so often employed in diagnoses, are 
useless. The exact temperatures must be quoted, and they must not 
be allowed to vary. 
In many cases, the emerging colonies form extremely thin films on 
the gelatine-surface, the play of light on which gives the iridescence so 
often quoted as a character. These films may consist of contorted or 
coiled tresses of filaments, lying parallel on the flat surface, like coils 
of rope : if growth is so vigorous that these films become more than 
one filament thick, the iridescence may not appear: if local lique- 
faction occurs, the filaments may break up into isolated Bacilli in 
patches, and curious mottled or mosaic-like, or tortoise-scale-like 
patterns may occur. If the liquefaction is more vigorous, the whole 
film may be set in curious amoeboid movements, and rapidly extend 
over the surface of the gelatine. I have a whole series of forms which 
seem to connect extremes where liquefaction of ten per cent, peptone- 
gelatine is rapidly brought about (in forty-eight hours or less) by 
means of these creeping and almost invisible surface-films, with 
others where the hyaline film shows no movements and the segments 
remain connected in coiled filaments. 
The size — both length and thickness — of Bacilli may differ in 
different parts of the same colony ; and forms, usually described as 
non-motile, may often be shown to be motile under given conditions. 
