VETERINARY SCHOOL AT ALFORT. 387 
gauic tissues of animals, including quadrupeds, and in certain ani- 
mals of the inferior orders in the scale of zoology. 
The experiments which he has undertaken on the tegumentary 
tissue of insects and their larvae have proved, in the silk-worm, 
that the tissue which forms the external envelope of this cater- 
pillar is partly composed of an organic, membranous, and transparent 
matter, remarkable for its defying all change from certain che- 
mical agents which decompose and dissolve the integument of the 
superior animals. 
The substance which enters into the composition of this epi- 
dermoid membrane, and which has been distinguished by the 
name of entomaderme, is found in the numerous elastic vessels 
which are symmetrically distributed throughout the whole of the 
silk-worm. We sometimes meet with it in a state of greater 
condensation in the hard and horned portions of every insect in 
the arachnoides and crustaces, but not in the ascarides, which 
multiply and live in the intestines of herbivorous animals. 
A chemical examination of this organic substance has shewn to 
M. Lassaigne that it was azotee, but less so than the greater part 
of the organic tissues of vertebrated animals. 
This assertion has just been recently confirmed by M. Payen, 
who, in a memoir read at the Academy of Science on the 7th of 
August last, compared it with certain vegetable tissues with 
which it was physically analogous. 
In studying the action of potassium on the organic azote prin- 
ciples of the animal economy, the same Professor has been enabled 
to discover a method as simple as it is certain of detecting the 
presence of azote in the almost impenetrable particles of organic 
matter. This process rests on the production of cyanogene, when 
we calcine organic matter defended from the air, whether much 
or little impregnated with potassium. 
A great number of the organic tissues, and many animal pro- 
ductions, are liable, on account of the sulphur which they contain, 
to be rendered of a brown colour by contact with certain metallic 
preparations. This explains, as M. Chevreul has stated, the 
changes of colour which the wool sometimes takes, when placed 
in contact with carding- teeth formed of certain metals. 
In examining different tissues and products placed in contact 
with a solution of the protoxyde of lead in soda, which renders 
wool, hair, and horse hair, brown, producing in these substances 
sulphur of black lead, M. Lassaigne has observed that a certain 
number of animal substances do not experience any effect from 
this chemical agency ; while others, and those which number 
sulphur among their elements, turn brown. Among the former 
we notice silk, which has the property of not becoming coloured ; 
