98 
INTRODUCTION TO 
consists of various strata of complicated fibres, which 
admit of being separated from each other. It is 
from this skin that the hairs originate, and from wiiich 
they derive their nourishment. 
In regard to chemical composition, the external 
covering approaches to the nature of horn, hut it 
differs from that substance by the admixture of a 
peculiar substance, viz. chitine or entomoline. Por- 
tions of phosphate of lime and magnesia are also 
constituent ingredients, although they exist in small 
quantities. One of the peculiar properties of chitine 
is its insolubility in potass. “ Exhibited separately, 
which is very easy, by means of steeping horny parts 
in a solution of potass, it appears as an almost colour- 
less transparent substance, which becomes brown 
in nitric acid, and in the dry distillation produces no 
carbonate of ammonia, and therefore appears to 
contain no azote ; it burns without previously melting, 
but is soluble in boiling or heated sulphuric acid. 
“ Besides the above, small portions of albumen, a 
peculiar brown colouring matter, which dissolves in 
caustic potass, but not in boiling alcohol, as well as 
traces of phosphate of iron, have been found in the 
horny integument of insects, upon different analyses. 
The albumen belongs doubtlessly to the third tunic, 
as does the brown colouring matter to the mucous 
rete : to this, also, we attribute the chitine, where- 
by the true horny skin, namely, the epidermis, will 
scales : yet even these scales, according to Cuvier, obtain their 
colour from being, in the chrysalis, in a state of mucosity, 
similar to that which is found under the skin of the caterpillar. 
