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iiarity. I have not been able to discover any reason for this differ- 
ence. It cannot be due to a difference of species, nor to the elevation 
at which the trees are growing, nor to the temperature limits of the 
respective districts, as in other districts, at both higher and lower 
elevations, and higher and lower temperature limits, e>g., Mexico 
on the one part, and Ecuador on the other, the Castilloa trees pro 
duce a perfectly fluid latex. It is not impossible that the condition 
of the soil, and the annual rainfall may have some influence upon 
this point, but in the absence of any positive proof 1 prefer to leave 
this matter for the present undecided. 
The latex of Castilloa at the moment of issuing from the cuts 
forms an almost pure white, thick creamy mass, which, however, 
almost immediately begins to discolour, assuming at first a pale 
drab colouration, which, in the course of a very short time darkens 
into a brownish black. This phenomenon, which is at least one of 
the causes of the very bad colour of all the Central American rub- 
bers of the present day, in fact, of all the rubbers obtained from 
Castilloa elastica, I found to be due to the presence in the latex of 
an oxidising ferment (oxydase) and it is, therefore obvious that in 
attempting to produce a high-class, pure rubber from Castilloa 
latex the presence of this ferment has to be taken into consi- 
deration. 
The taste of the Castilloa latex is intensely bitter. This appears 
to be due to the presence in it of a substance of the class of bodies 
chemically described as glucosides. It is this same body which is 
the cause of the intense dark green colouration produced by the 
addition to the latex, or better to its aqueous vehicle, of a few drops 
of a solution of ferric chloride. I presume that this reaction has 
been observed before, and led the observers to the altogether er- 
roneous assumption that the Castilloa latex contains tannic acid, 
which latter as is well known, produces much the same colouration 
with ferric-chloride. As a matter of fact, there is not the slightest 
trace of tannic acid to be found in this latex, and I doubt whether 
it occurs in the latex of any other rubber tree. It is really only 
necessary to state that the latex of Castilloa elaslica, beside the 
bodies already named, contains a very large proportion of albumen, 
and to remind the reader that albumen may be quantitatively pre- 
cipitated with tannic acid, in order to prove that the presence of 
tannic acid in the latex is an impossibility. Indeed, on adding to 
solution of the aqueous vehicle of the latex of Castilloa a few 
drops of a dilute solution of tannic acid, a most copious precipitate 
of albumen tannate is at once obtained. Considering that all the 
different specimens of rubber latex I have so far an opportunity 
of examining contain albumen in varying quantities, though none 
as much as the latex of Castilloa elastica, is at the same time suffi- 
cient proof of the absence of tannic acid in every case, 
A quantitative determination cf the amount of albumen and 
albuminous matters in general in the latex yielded the rathrr sur- 
prising result that there is as much as 1 1 per cent, of these bodies 
present. This, I believe, is the cause of the extreme ease with 
which the latex of Castilloa elastica can be coagulated. I am quite 
