COMPOUNDS OF ORGANIZATION. 59 
These simple substances have been detected by chemists 
in the solids and fluids of animals; but seldom, as we have 
said, in a free state. Many of them combine, in such va- 
rious proportions, that it is extremely difficult to determine 
their true condition, or fix the characters of their natural 
and permanent results. Without entering into detail, we 
shall briefly enumerate these various compounds; the me- 
thods of procuring them in a separate state; the characters 
by which they are distinguished ; and their uses in the ani- 
mal economy. 
II. CompounnDs oF ORGANIZATION. 
1. Gelatine.—This substance occurs, in nearly a pure 
state, forming the air-bag of different kinds of fishes, and 
well known in commerce under the name isinglass. When 
in a dry state, it is colourless and translucent ; yields with 
difficulty to the knife; and, upon being broken, exhibits 
a resinous lustre, and conchoidal fracture. 
When thrown into cold water, it becomes soft and in- 
creases in bulk, but does not readily dissolve. Hot water 
dissolves it in large quantities. ‘The solution is translu- 
cent ; of an opal colour; and gelatinizes as it becomes cold. 
In this state it is well known by the name of Jelly. Che- 
mists term it ¢remulous gelatine. When in a dry state, ge- 
latine may be kept for any length of time; but, when thus 
united with water, it very soon putrifies. Specimens pro- 
cured from different substances, appear to vary consi- 
derably, even in the dried state, in the quantity of 
water which they retain. Those which contain the great- 
est quantity form the least viscid solutions; while those 
which contain the least, form solutions which are strong 
and tenacious. Acids dissolve this substance with facility, 
and form compounds whose properties have not been exa- 
mined with much care.  Alkalies likewise dissolve it 
