8 EVOLUTION AND DISEASE. 
and dies. The branches suffer first and then the 
beam. At this stage the antlers become formidable 
weapons, and the stag, instead of taking every precau- 
tion not to knock or bruise them, now fears nothing, 
for they are like dead bone, devoid of sensation. In 
time the necrosis extends along the antler until it 
reaches the pedicle, that part which is covered by the 
natural hairy skin of the deer; in due course a line of 
demarcation is formed by leucocytes, and the antler falls 
Fic, 4.—The head of a Cow with a large cutaneous horn. 
by a process exactly analogous to that by which a piece 
of dead bone is separated. 
We may turn to the consideration of processes in 
disease which are dominated by the physiological pro- 
cesses peculiar to a particular animal, and _ illustrate 
this by reference to cutaneous horns, especially that form 
which arises from the modification of warts. Not in- 
frequently in mammals and birds the free portions of 
