6 EVOLUTION AND DISEASE. 
rounded or irregular swelling termed a node. In some 
cases the periosteum is so damaged that it becomes 
detached, and as a consequence the bone beneath dies. 
As soon as a piece of bone is dead those parts of the 
living bone adjacent become unusually active, leucocytes 
or white-blood cells begin to devour and finally succeed 
in detaching the dead portions when large, or digest 
them completely when small. Dead bone is known 
by the following features—it has no sensation, emits a 
sound when struck with a metallic instrument, and does 
not bleed when cut. 
The antlers of deer when young and growing are 
covered with a soft vascular membrane, beset with 
delicate downy hair and glands, termed the “ velvet,” 
which bears the same relation to growing antlers that 
periosteum holds to bone (fig. 2). As long as the 
antlers retain this velvet in a living condition they 
increase in length and thickness ; when the antlers are 
actively growing they feel warmer to the hand than the 
rest of the body, resembling in this respect an in- 
flamed part. When in “velvet” a stag is particu- 
larly careful not to knock the antlers, for they are very 
sensitive, and when so unfortunate as to bruise them, 
a node or swelling forms upon them in every way 
resembling nodes on other bones when injured. I have 
seen nodes on antlers, caused by blows, as large as 
oranges. This is illustrated in fig. 3, which is a drawing 
of a pair of antlers of a roe-deer preserved in the 
museum of the Royal College of Surgeons. The left 
antler is shorter than the right one and has an ossified 
node upon it as large as a Tangerine orange. After the 
