1644 
group rendered active by exposure to light, as found by us, now 
enables us to obtain a series of aldehydes in a perfectly neutral 
medium. 
Here, however, it must be observed that the alcohol should not 
cause a hindrance. 
It appeared for instance that citronellol, although a primary alcohol 
with a double bond far removed from the OH-group was not 
oxidised; this now must be attributed to a disturbing influence exerted 
by the alcohol on the active light. 
If we place this alcohol in the jacket of the mantle tube (see 
previous communication), it also retards the reduction of benzophenone 
by ordinary alcohol in the inner tube. 
Even with strong sun-light in the spring the velocity of the reaction 
is but small: this can only be remedied by enlarging the surface 
illuminated. If we wish to become independent of the sun-light 
powerful mercury lamps will have to be used with the reaction 
mass in a jacket round the are light. 
For practical purposes we do not consider the photo-reaction to 
be of much importance just yet, but from a theoretical point of 
view it is so all the more. 
This now may appear from the following points: 
1st. It has been shown that, among all other primary and secon- 
dary, saturated alcohols, the methyl alcohol occupies a special place 
because reaction with benzophenone and its derivatives takes place 
much slower (see previous communication). 
This is based on a lesser activity of the H-atoms of the alcohol 
towards the oxygen and not, as in the case of citronellol, to an 
absorption of active rays. 
Therefore, we can understand that also the physiological action 
of this aleohol must be different from that of its analogues. This 
difference has been found with the human being as well as with 
penicillium glaucum. 
2nd. When we consider the succession of the photo-reactions which 
from the mixture of aromatic ketone and alcohol lead to pinacone 
and aldehyde we find some resemblance to the assimilation process. 
Of the latter we can very roughly conceive the following image : 
I. (chlorophyllogen + protoplasm) + little light = (chlorophyll + 
protoplasm). 
II. (chlorophyll + protoplasm + carbon dioxide) + more light = 
(chlorophyll + protoplasm + formaldehyde) + Q,. 
