Chemical Action of Light. 
479 
1885.] 
VI. ON THE CHEMICAL ACTION OF LIGHT. 
8 DROF. A. VOGEL, in a communication to the “ Sit- 
p zungsberichte der Miinchener Akademie,” brings into 
piominence the faCt that the hemlock plant which 
yields coniine in Bavaria contains none in Scotland. 
Hence he concludes that solar light plays a part in the 
geneiation of the alkaloids in plants. This view is corro- 
borated by the circumstance that the tropical Cinchonas, if 
cultivated in our feebly lighted hothouses, yield scarcely 
any alkaloids. Prof. Vogel has proved this experimentally. 
He has examined the barks of Cinchona plants obtained 
from different conservatories, but has not found in any of 
them the characteristic reaction of quinine. Of course it 
is still possible that quinine might be discovered in other 
conservatory- grown Cinchonas, especially as the specimens 
operated upon were not fully developed. But as the re- 
action employed indicates very small quantities of quinine 
it may be safely assumed that the barks examined contained 
not a trace of this alkaloid, and it can scarcely be doubted 
that the deficiency of sunlight in our hothouses is one of the 
causes of the deficiency of quinine. 
It will at once strike the reader as desirable that speci- 
mens of Cinchonas should be cultivated in hothouses under 
the influence of the eleCtric light, in addition to that of 
the sun. 
If sunlight can be regarded as a faCtor in the formation 
of alkaloids in the living plant, it has, on the other hand, a 
decidedly injurious aCtion upon the quinine in the bark 
stripped from the tree. On drying such bark in full sun- 
light the quinine is decomposed, and there are formed 
dark-coloured, amorphous, resin-like masses. In the ma- 
nufacture of quinine the bark is consequently dried in 
darkness. 
This peculiar behaviour of quinine on exposure to sun- 
light finds its parallel in the behaviour of chlorophyll with 
the direCt rays of the sun. It is well known that the origin 
of chlorophyll in the plant is entirely connected with light, 
so that etiolated leaves growing in the dark form no 
chlorophyll. But as soon as chlorophyll is removed from 
the sphere of vegetable life, a brief exposure to the direCt 
rays of the sun destroys its green colour completely. 
