8 
MR. J. BROUGHTON’S CHEMICAL AND PHYSIOLOGICAL 
The above was made with young bark whose liber contained parenchymatous as well 
as woody cells. In older bark the difference would be still more marked. The fact of 
the quinine being contained mainly in the exterior cellular tissue is in harmony with its 
occurrence in newly forming structures, as detailed above.' 
I have never yet succeeded, although many attempts have been made, in converting 
quinine into cinchonidine, or vice versa. Nevertheless many phenomena in the living 
plant point to the conclusion that a real change of quinine into cinchonidine occurs 
therein. The order of the appearance of the alkaloids in renewing bark, the compara- 
tive absence of quinine in the highly organized liber, the changes produced by sunshine 
and heat, all point to such conversion as a legitimate hypothesis ; it is one that is not 
contradicted by a single fact, and is in harmony with observations made with very diverse 
species of cinchona, and with the chemical similarity in the behaviour and properties of 
the two substances. 
Influence of Sunlight and Heat on growing Cinchona-lark. 
Pasteur* first pointed out that quinine, cinchonine, &c. are converted, under the 
influence of a high temperature, into the isomeric uncrystallizable alkaloids, quinicine 
and cinchonicine. He also showed that the same change was effected by exposing the 
salts of the alkaloids to sunshine. On these grounds he asserted that the plan of drying 
cinchona-bark in the sunshine, as practised in South America, is injurious to its quality. 
Many experiments made during the last two years have amply corroborated these 
assertions. The purest and whitest alkaloids I have been able to prepare become coloured 
brown when exposed to the Indian sunshine, and the change is still more rapid when 
exposed in the form of salts. All the four alkaloids are affected in the same manner, 
even when sealed in vacuo, but the change is more readily effected in the case of the 
salts of quinine. In the solid state the change is very superficial ; and in cases where the 
uncrystallizable alkaloids are formed more abundantly, the amount produced is only a 
small percentage of the whole, even when the insolation has lasted weeks. Pure quinine 
sulphate is especially sensitive to light, but becomes far less so when a small amount of 
the corresponding salt of cinchonidine is present, as frequently is the case in the com- 
mercial salt. 
In the course of a long series of experiments made to determine the best practical 
method of drying the bark for export, the effects of heat and sunshine were abundantly 
manifest. The change produced by sunshine on the bark requires some time to become 
very perceptible. It is thoroughly apparent when the drying of the fresh bark is 
checked by exposing it for a fortnight in a box covered with glass ; a decrease in the 
yield of the crystalline sulphates then becomes clearly evident, and amounts to from 0-8 
to IT per cent, of the dried bark. If the bark be finely shred (to increase the surface 
of action) and exposed for three days to the cloudless Indian sun, the alkaloids also lose 
the power of crystallization to the amount of 0-6 per cent. In both cases I have never 
* Comptes Rend, vol. xxxvii. p. 110. 
