422 MR. A. J. EWART ON ASSIMILATORY INHIBITION. 
very slow rotation still persists. In 20-30 minutes rotation also 
ceases. If now a rapid current of hydrogen is passed through 
till only mere traces of CO, are left, in 5 minutes a distinct 
evolution of oxygen is shown and slow rotation has commenced. 
In 15 minutes the evolution of oxygen is quite active, and in 
half an hour rotation is also quite active. In such experiments 
no external supply of oxygen reaches the filaments, and if 
Pringsheim's contention that free oxygen is never present in the 
interior of a cell were true, then this would be a case in which 
.a recovery of both assimilation and rotation takes place without 
any oxygen being supplied from without, the oxygen necessary 
for the performance of rotation as well as of the other proto- 
plasmic functions being supplied from the first by the assimila- 
tion of the cell itself. The experiment is, however, faulty, 
because the stoppage of the protoplasmic activity is due to a 
direct poisonous influence of the CO,, and certainly takes place 
before the amount of free or loosely held oxygen present in the 
cell is reduced to its lowest ebb. It is quite possible that, if 
this latter condition were actually produced, no return or re- 
‘commencement of rotation or assimilation (taking for granted 
that in some of its stages at least assimilation is a plasmatic 
function) could occur without being started by a supply of 
oxygen from without. Such a condition, in which all free or 
loosely combined oxygen in the cell is removed down to the last 
molecule, seems to be rather a theoretical than a practical one, 
being impossible to produce without at the same time destroying 
the protoplasmic vitality. 
There can be little doubt that assimilation is largely if not 
mainly a protoplasmic funetion, and that the chlorophyll pigment 
is simply a cooperative member in the assimilatory apparatus of 
the living chlorophyll body. Whether the function is located 
entirely in the plasmatic stroma of the chlorophyll grains, or 
also partly in the protoplasm immediately surrounding these, or 
in the general protoplasm of the cell, is immaterial to the 
question at issue, though all the evidence goes to show that 
assimilation in the special sense is restricted entirely to the 
chlorophyll grain. Of all the different modes of inhibiting 
assimilation described in the previous pages, two only are accom- 
panied by a change in the colour of the chlorophyll, viz. the 
winter browning of evergreens and the effect of antipyrin on 
