NUTRITIVE PRINCIPLES OF PLANTS. 259 
to that ingredient of the seeds of the cereals which is entirely in- 
soluble in water, because different names must be given to bodies 
in different conditions, and the idea of solubility in certain liquids, 
and coagulation by heat, is inseparably connected with albumen. 
This substance approaches the fibrin of the blood in all its pro- 
perties, and all its relations to other bodies: the ashes contain 
no soluble alkali, whereas, all liquids which contain albumen, 
such as the serum of the blood, leave a great deal of alkaline 
carbonates when dried and burnt. The presence of an alkali 
may be the cause of its solubility in one case, and the absence 
of an alkali the cause of its insolubility in another; but the al- 
bumen of the serum, and the fibrin of the blood, owe their dif- 
ferent conditions to the same cause. For this reason, and to 
avoid the extraordinary confusion observable in the usual de- 
scriptions of these bodies, which so greatly resemble each other, 
I have adopted the name of vegetable fibrin, to distinguish this 
insoluble modification, although it may not appear altogether 
appropriate. 
Vegetable albumen, fibrin, and casein, dissolve in warm con- 
centrated hydrochloric acid, with the same lijac or violet colour, 
as the corresponding animal substances; when heated alone, 
they give the same sulphurous products, and the same horny 
ammoniacal smell. 
When left moist they putrefy ; the products of the putrefaction 
of gluten and vegetable fibrin are in some measure known, and 
differ from those of caseum by evolving gas at the beginning, 
like flesh. Caseum does not do so, but the same solid products 
are found in both cases; they have the taste and smell of caseum, 
freed from butter, and as much aposepedin, or, as Gmelin terms 
it, oxide of caseum, may be obtained from it, in fine, bright 
scales, like mother of pearl, as from caseum. 
Vegetable casein possesses in a high degree the power of 
fermenting sugar, if it is allowed to stand until putrefaction 
has commenced. If allowed to stand till putrefaction has made 
some progress, it is impossible to distinguish it from common 
caseum ; and vegetable albumen gives out sulphuretted hydrogen 
exactly as the rotten egg. It is not very improbable that casein 
is contained, in a state of solution, in the juice of grapes and 
those plants which precipitate very little albumen on being 
heated and evaporated. It is known to be very soluble in tar- 
taric acid, and the presence of this acid may be the reason that 
