372 
Notices of Books and Papers . 
if any, exists between the assimilation of carbon by green cells and 
the supply of free oxygen, and (2) to ascertain the seat of origin of the 
oxygen evolved in connection with the assimilation of carbon. In 
order to attain this object, it was essential to possess means, both 
within and without the living cell, of determining the presence of free 
oxygen. For the latter purpose the Bacterium-method was employed ; 
for the former, Prof. Pringsheim devised a method of his own, namely, 
the observation of the rotation or circulation of the protoplasm in the 
cell. Since it is known that these movements depend upon a supply 
of free oxygen, it is clear that their arrest or resumption may be taken 
as an indication of the absence or presence of this gas. It was further 
essential to control the composition of the atmosphere. This was 
done by observing the cells in a closed chamber through which a cur- 
rent of the required mixture of gases was kept passing. The objects 
used were the leaflets of Chara , the terminal cell being especially 
observed. They were examined suspended in a hanging drop of 
water. 
The general nature of the experiments may be briefly summarised 
as follows : — 
1. When the cell was deprived of a supply of free oxygen, the mix- 
ture of gases passing through the chamber consisting of hydrogen 
with 10 % carbon dioxide (in some cases 3-5 %), and was kept in 
darkness, the rotation of the protoplasm was arrested sooner or later 
(2-10 hours). Prolonged exposure in the atmosphere of H and C 0 2 
caused death (Asphyxia) ; but when oxygen was admitted to the 
chamber soon after the protoplasmic movements had ceased, the 
movements were resumed. 
2. When a cell in which rotation had just ceased was exposed to 
light in the same atmosphere (C 0 2 and H), the rotation was not re- 
sumed : but was readily resumed on admitting air into the chamber. 
Hence it appears that the period of existence in an atmosphere con- 
taining no free oxygen which causes the arrest of rotation, induces also 
a condition of the protoplasm in which it is incapable of assimilating 
carbon. This condition of 4 nutritive incapacity ’ ( Ernahrungs - 
ohnmacht ), Pringsheim terms Inanition . No evolution of oxygen 
from a cell in this condition can be detected by the Bacterium- 
method. 
3. When a cell was kept continuously exposed to light in the atmo- 
sphere of C 0 2 and H, rotation eventually ceased, much as in darkness, 
