ITS FORMATION 
359 
say an etiolated caoutchouc. The humidity of the soil seema 
to account for the undulating form of the edges of the 
dapicho, and its division into layers. 
I often observed in Peru, that on pouring slowly the 
milky juice of the hevea, or the sap of the carica, into a 
laro-e quantity of water, the coagulum forms undulating 
outlines. The dapicho is certainly not peculiar to the 
forest that extends from Javita to timichin^ although that 
is the only spot where it has hitherto been found. I have 
no doubt, that on digging in 1'rench Guiana beneath the 
roots and the old trunks of the hevea, those enormous 
masses of corky caoutchric,* which I have just described, 
would from time to time be found. As it is observed m 
Europe, that at the fall of the leaf the sap is conveyed 
towards the root, it would be curious to examine whether, 
within the tropics, the milky juices of the urticese, the 
euphorbiacese, and the apocyne®, descend also at certain 
seasons. Notwithstanding a great equality of temperature, 
the trees of the torrid zone follow a cycle of vegetation; 
they undergo changes periodically returning. The existence 
of the dapicho is more interesting to physiology than to 
vegetable chemistry. A Yellowish-white caoutchouc is now 
to be found in the shops, which may be easily distinguished 
from the dapicho, because it is neither dry like cork, nor 
friable, but extremely elastic, glossy, and soapy. I lately saw 
considerable quantities ot it in London. This caoutchouc, 
white and greasy to the touch, is prepared in the East 
Indies. It exhales that animal and fetid smell which [ 
have attributed in another place to a mixture of caseurn 
and albumen.f When we reflect on the immense variety 
* Thus, at five or six inches depth, between the roots of the Hymenea 
courbaril, ’masses of the resin anime (erroneously called copal) are dis- 
covered, and are sometimes mistaken for amber in inland places. This 
phenomenon seems to throw some light on the origin of those large masses 
of amber which are picked up from time to time on the coast of Prussia. 
' + The pellicles deposited by the milk of heavea, in contact with the 
atmospheric oxygen, become brown on exposure to the sun. “ the 
dapicho grow black as it is softened before the fire, it is owing to a slight 
combustion, to a change in the proportion of its elements, i am 
surprised that some chemists consider the black caoutchouc ot commerce 
as being mixed with soot, blackened by the smoke to which it has been 
exposed. 
