12 
ME. J. BROUGHTON'S CHEMICAL AND PHYSIOLOGICAL 
is also evident in the more hardy C. officinalis. Many other analyses of cinchona-bark 
grown at low elevations have abundantly shown that a high mean temperature is adverse 
to the production of quinine. These results, taken in conjunction with those obtained 
from shielded hark, seem to demonstrate that sunlight degrades the alkaloids generally, 
while heat mainly diminishes the amount of quinine. 
It would naturally be expected that, as the barks become thickened with age, the sun- 
light would produce a less marked effect; this is exactly what occurs. Up to the pre- 
sent time the amount of alkaloids has annually increased in the bark. In the C. succi- 
rubra this increase has been determined as carefully as the conditions permit, and the 
increments during the sixth and seventh years have been 075 and 05 per cent, respec- 
tively. That some part of this increase is due to the inability of sunlight to affect the 
lower-seated tissues, appears certain from the fact that mossing or otherwise shielding the 
bark has a less effect in increasing the amount of alkaloids in the older bark than in the 
thin bark of younger trees. There is every reason to think that the alkaloids will 
increase by annually diminishing amounts until the amount formed is only equivalent 
to the destructive influences at work. The growth of the liber and the formation of 
woody cells, for the reasons given above, is adverse to the increase of yield of alkaloids. 
In connexion with this subject it should be mentioned that trees of C. officinalis , 
growing in dry sunny spots, almost invariably produce bark whose main alkaloid consti- 
tuent is cinchonidine. The trees grown in shade produce more quinine. The bark 
of trees of rapid and vigorous growth of the same species invariably contain a large 
amount of alkaloid, and an unusually large proportion of quinine. The latter case can 
be readily explained by the foregoing principles. The bark of such would be thicker, 
would contain much parenchymatous tissue, and would, by its more rapid formation, have 
been exposed for a less time to the deteriorating influences of the sun. It is very 
remarkable that trees of vigorous growth should yield not only more bark, but also bark 
in which one hundred parts should contain double the amount of alkaloids. 
All cinchona-barks contain small amounts of ammonia. As it is not improbable that 
ammonia is a stage in the formation of alkaloid, a set of experiments has been com- 
menced as to the action of ammoniacal manure on the yield of alkaloids in the bark ; 
they are, however, not sufficiently advanced to be here detailed. 
The Alkaloids considered as substitutes for Mineral liases. 
A speculative opinion has long been held concerning the functions of the vegeto-alka- 
loids in the plants producing them, whose importance is so great that its practical veri- 
fication or contradiction is a primary necessity to a scientific theory of the formation of 
the alkaloids. The hypothesis alluded to is a corollary to the “ mineral theory” of 
Liebig, and has been indirectly enunciated by that chemist himself (Chemistry in its 
Applications to Agriculture, p. 187). 
According to this hypothesis, the alkaloids are substitutes for certain of the mineral 
bases which are the constituents of all plants, and which constitute the larger portion of 
