318 ANATOMY AND PHYSIOLOGY OF THE HORSE’S FOOT. 
than the sole. The whole, nevertheless, is absorbent, and 
becomes softened by the imbibition of moisture. This faculty 
appears to he increased when the hoof has been removed from 
the foot ; though this is only apparent, for the vascular parts 
it contains during life keep its inner layers moist, and then of 
course it does not take up so much fluid. A hoof containing the 
bones and soft parts, and which had been immersed for four 
days in water, was only increased in weight by eight tenths of 
a drachm. When exposed to heat it loses its humidity, con- 
tracts on itself, decreases in volume, becomes hard and dry, 
and its porosity is diminished. 
Like all other horny substances, this of the hoof is a bad 
or slow conductor of heat ; but this quality again differs in 
different parts, the wall transmitting heat less slowly than the 
sole. Experiments made in 1845 showed that it took from four 
to five minutes’ burning of the wall and sole, possessed of their 
natural thickness, with a red-hot iron, before a thermometer 
applied to the opposite face testified to the transmission of 
the heat. Horn is readily combustible ; a high temperature 
first softens, then fuses it, and its continuation causes it to 
burn, in doing which it emits a dense smoke having an 
empyreumatic odour. By roasting, it yields carbon and the 
hydrosulphate of ammonia. 
It is softened by alkaline substances, as caustic, potash, 
soda, or ammonia, and prolonged action of these reduces it to 
a gelatinous mass. The parts first attacked are the com- 
missures, then the frog, and afterwards the sole and -wall ; 
the latter withstanding the solvent action longest at the toe 
or centre. Strong acids, such as sulphuric and nitric acid, 
also dissolve it. The sulphuric is less potent than the nitric 
acid. The latter rapidly acts upon it, changing it into a 
yellow earthy powder. Hydrochloric acid has the same effect 
as the caustic alkalies. 
The chemical composition of hoof shows that it is a 
modification of albumen, its analysis yielding water, a large 
per centage of animal matter, and matters soluble and in- 
soluble in water. 
The proportions of these are not the same in the wall, sole. 
and frog, and their 
relations have 
been given 
by Professor 
Clement, of Alfort, 
as follows : 
Wall, 
Sole. 
Frog. 
Water . 
. 1612 
36-00 
42-00 
Tatty matter . 
. 0-95 
0-25 
0-50 
Matters soluble in water . 104 
1-50 
1-50 
Insoluble salts 
> . 0-26 
0-25 
0-22 
Animal matter 
. 81-63 
62-00 
55-78 
