366 MR. A. J. EWART ON ASSIMILATORY INHIBITION. 
in a properly ringed and closed cell, then the culture is impure, 
and anerobic forms, which can move in the absence of oxygen 
if food material be present, or partial ærobes, such as certain 
Spirilla, which can move in the presence of an infinitesimal trace 
of oxygen, are present. The Bacterium Termo form used, in 
ordinary tap-water, containing a slight percentage of salts and 
but a mere trace of nutriment, continues to move as long as 
oxygen is present, and may remain living and motile in the 
absence of oxygen for 1 or 2 days, moving as soon as oxygen 
is admitted or generated. The sensitivity of the Bacteria, 
however, undergoes, with regard to oxygen, in 12 hours a 
distinct, and in 24 hours a marked alteration, they becoming less 
sensitive to the absence and more sensitive to the presence of 
minute traces of oxygen, i.e. partial starvation increases their 
sensitivity to oxygen. Finally, in the absence of all nutriment, 
B. Termo ceases to move in the presence of oxygen and becomes 
quite immotile. The maximal and minimal temperatures for 
movement are widely separated, the optimum temperature lying 
between 15? C. and 30? C. Above and below these limits the 
movement is uot quite so active, but continues quite actively in 
the presence of oxygen on the one hand as far as zero, and on 
the other up to 40? C. 
When a cell or tissue is examined by the Bacterium method to 
detect the presence or absence of the power of assimilating and 
evolving oxygen, it is naturally important to determine, espe- 
cially if comparative experiments are to be made, to what extent 
the evolution of oxygen from the free surface of the cell is 
modified by the nature of the enclosing cell-membranes or by 
the surrounding fluid. Is, for example, oxygen evolved more 
rapidly through uncuticularized than through cuticularized epi- 
dermis? To settle this point, isolated hairs of Gynura aurantiaca 
‘were examined in a closed cell with Bacteria exposed to light. The 
hair-cells contain a purple dye dissolved in the cell-sap, which fades 
as the hair grows older, and in the lining plasma rather small and 
not abundant chlorophyll grains are present. A distinct though 
not strong evolution of oxygen is shown by all normal chlorophyll- 
containing hairs, whether the sap is purple or colourless. If the 
hair has separated exactly at the partition-wall between two cells, 
it can be seen that the evolution of oxygen takes place with equal 
activity from all surfaces of the cell. If the torn remains of a 
basal cell remain attached to the lower end of the hair, the 
