45 8 ON GUTTA PERCHAj &C. 
By this admixture various sorts of gutta percha are obtained, 
which differ considerably in price. 
Examination of the Milky Juice of Ficus Elastica . — The 
author had the opportunity to examine the fresh milky juice of 
Ficus Elastica (from which, as from other species of Ficus , 
caoutchouc is manufactured in the East Indies) from a plant of 
two-and-a-quarter metres high, which, even after extracting 
part of the juice, remains in a good condition in the botanical 
gardens of Utrecht. The milky juice was obtained by cutting 
off branches or leafstalks, and successively introducing the cut 
ends into small vessels, and allowing the juice to flow out. The 
author then found, that the nearer the part from which the 
milky juice was drawn was to the upper end of the plant, the 
larger was its proportion of water. That drawn from a terminal 
bud contained 17.7 per cent, solid substance; that which issued 
closely beneath the latter contained 20.98 ; and that drawn 
from a leafstalk thirty centimetres above the ground, 25.15. 
Corresponding with this proportion, the milky juice from the 
upper parts appears to be less milky and more aqueous than 
that from the inferior parts. The fresh milky juice has an acid 
reaction, and under the microscope appears to consist of a clear, 
aqueous fluid, in which float a large number of globules of small 
diameter, and consisting of caoutchouc. By mixing the juice 
with water, no change takes place ; on the addition of alcohol, 
a large number of small crystalline needles are precipitated, 
which unite in groups: ether causes the globules to unite, whilst 
the same needles are forming as with alcohol. Nitric acid pro- 
duces a slight white precipitate, which is not dissolved by am- 
monia; ammonia or potash colours the liquid yellowish; tinc- 
ture of iodine colours the globules brown, and causes them to 
combine together to form larger viscid drops. Being dried on 
a glass plate, the juice leaves a membraneous coating behind, 
in consequence of the union of the caoutchouc drops. 
The author found, upon a continued microscopic analysis, that 
the juice from the terminal buds consists of 
Water 82.30 
Caoutchouc 9.57 
Resin, soluble in alcohol, but not in ether . . . . 1.58 
of an organic acid, and a substance (sugar?)) ~ 
soluble in water and alcohol, but not in ether . . / 
A substance soluble in water, becoming yellow by alkalies,) 9 
(dextrin?) traces of / 
100.48 
The organic acid, whose magnesian salt forms, on the addi- 
tion of alcohol and ether, crystals, does not appear to have any 
analogy with the known organic acid. Its most remarkable 
