52 
AXALTSIS OF VEGETABLE MILK 
I have endeavoured by these comparisons to bring into 
consideration, under a more general point of view, the milky 
juices that circulate in vegetables ; and the milky emulsions 
that the fruits of the amygdalaceous plants and palms yield. 
I may be permitted to add the result of some experiments 
which I attempted to make on the juice of the Carica 
papaya during my stay in the valleys of Aragua, though 
I was then almost destitute of chemical tests. The juice 
has been since examined by Vauquelin, and this celebrated 
chemist has very clearly recognized the albumen and caseous 
matter ; he compares the milky sap to a substance strongly 
animalized, — to the blood of animals; but his researches 
were confined to a fermented juice and a coagulum of a 
foetid smell, formed during the passage from the Mauritius 
to France. He has expressed a wish that some traveller 
would examine the milk of the papaw-tree just as it flows 
from tbe stem or the fruit. 
The younger the fruit of the carica, the more milk it 
yields : it is even found in the germen scarcely fecundated. 
In proportion as the fruit ripens, the milk becomes less abun- 
dant, and more aqueous. Less of that animal matter which 
is coagulable by acids and by the absorption of atmospheric 
oxygen, is found in it. As the whole fruit is viscous,* it 
might be supposed that, as it grows larger, the coagulable 
matter is deposed in the organs, and forms a part of the 
pulp, or the fleshy substance. When nitric acid, diluted 
with four parts of water, is added drop by drop to the milk 
expressed from a very young fruit, a very extraordinary phe- 
nomenon appears. At the centre of each drop a gelatinous 
pellicle is formed, divided by greyish streaks. These streaks 
are simply the juice rendered more aqueous, owing to the 
contact of the acid having deprived it of the albumen. At 
the same time, the centre of the pellicles becomes opaque, 
and of the colour of the yolk of an egg ; they enlarge as if 
by the prolongation of divergent fibres. The whole liquid 
* The same viscosity is also remarked in the fresh milk of the 
palo de vaca. It is no doubt occasioned by the caoutchouc, which it 
not yet separated, and which forms one mass with the albumen and the 
caseum, as the butter and the caseum in amimal milk. The juice of a 
euphorbiaceous plant (Sapium aucuparium), which also yields caoutchouc 
is so glutinous that it is used to catch parrots. 
