374 
Notices of Books and Papers. 
dioxide in respiration. In support of this view he cites cases in which 
he has observed that parts of plants, whether or not containing chloro- 
phyll, evolve oxygen in darkness (indicated by the Bacterium-method) 
as they gradually die ; in which there is a sort of c intramolecular ’ 
evolution of oxygen, just as there is an c intramolecular ' evolution of 
carbon dioxide in parts of plants when cut off from a supply of free 
oxygen. 
This line of argument is, however, by no means conclusive. One 
of his own facts militates strongly against it ; the fact, namely, that, in 
cells continuously exposed to light, the rotation continued, in most 
cases, for a longer time than the evolution of oxygen, which would 
seem to indicate that oxygen was set free in the interior of the cell for 
some time after it had ceased to be evolved at the surface. This fact 
might be explained away by assuming that the rotation is maintained 
by intramolecular respiration, but such an explanation is quite at 
variance with what is known as to the physiology of these protoplasmic 
movements, and it is rejected by Professor Pringsheim himself. 
Again, the phenomenon which this new theory is especially designed 
to explain, the phenomenon of the gradual arrest of movement and the 
induction of inanition in a cell exposed continuously to light in an 
atmosphere of hydrogen and carbon dioxide, may be explained, and 
apparently in a satisfactory manner, by means of a less hazardous 
assumption. It involves no great stretch of the imagination to sup- 
pose that, in consequence of there being a continuous current of 
hydrogen and carbon dioxide passing through the chamber, the 
oxygen was removed from the cell more rapidly than it was produced, 
so that eventually no free oxygen was present, and that then arrest of 
movement and inanition were induced. 
It is true that, in some cases, the phenomenon necessary to prove 
the truth of the theory was observed ; the phenomenon of the arrest 
of the rotation in the cell before the cessation of the evolution of oxy- 
gen at the surface, as indicated by the Bacterium-method. But these 
cases constitute only a minority of the observations. It is therefore 
impossible to accept the second of Professor Pringsheim’s conclusions 
without more convincing evidence. 
S. H. V. 
