1 34 Notes on Recent Physiological Literature 
judgment is inevitable. The great pitfall of this class of work 
seems to be the neglect to do elaborate and thorough control 
experiments so that every imaginable cause except the alleged one 
is excluded, and we hope these authors will not rest satisfied with 
their excellent start, but will thresh out the whole matter. 
Turning to the state of affairs in the green cell, Usher and 
Priestley are able to put forward a complete scheme of the stages 
of the reduction of C0 2 . The form of this is simple and reasonable 
and is supported by some experimental evidence at each step. If 
further experiments render this interesting scheme proof against all 
attack, it will be a very noteworthy advance in the chemical analysis 
of those processes which were formerly lumped together as “ proto¬ 
plasmic.” 
Three separable stages in photo-synthesis are suggested. (</) 
CO 2 + Water is converted to formaldehyde + hydrogen peroxide, 
the chlorophyll acting as an optical sensitiser; this stage is held not 
to involve the vitality of the cell, (b) The formaldehyde is removed 
and condensed to a sugar by the action of the protoplasm, (c) The 
hydrogen peroxide is removed by being split up by an enzyme to 
water and oxygen, the latter being set free in the gaseous form. 
The experimental evidence, chiefly from Elodea, put forward on 
the various stages may be briefly indicated. Formaldehyde actually 
is formed in green cells, as various tests show. It can best be 
demonstrated when the protoplasm has been killed, as then it is not 
removed and condensed. In boiled leaves, lacking both enzyme and 
protoplasm, the hydrogen peroxide also accumulates and soon 
bleaches the chlorophyll. In chloroformed leaves, the enzyme 
remains and at first splits up the hydrogen peroxide, but after a time 
the accumulating formaldehyde “poisons” the enzyme and stage (c) 
also ceases. If Elodea leaves be put in solution of hydrogen peroxide 
the green cells decompose it freely and bubbles of oxygen arise. 
In a second quite recent communication,' Usher and Priestley 
state (i.) that a very thin film of concentrated chlorophyll will by 
itself decompose C0 2 in sunlight, (ii.) that if this film be superposed 
on a film of gelatine containing the right enzyme, oxygen is evolved 
from the C0 2 and the formation of formaldehyde is demonstrable. 
Thus the whole reduction-process is non-vital and the protoplasm 
only comes in to condense the formaldehyde to sugar. 
There is one rather important general consideration which 
seems to the writer to be opposed to the view that the formation of 
formaldehyde in the cell is outside the activity of the protoplasm. 
1 Communication to the Royal Society, May 10th, 1906. 
