BLACKCOCK—BLOOD 43 
superfluous. Enough to say that its tones always brought to his 
mind the lines in 4s You Like It (Act ii. se. 5): 
“ And turn his merry note 
Unto the sweet bird’s throat.” 
The name, however, is only applicable to the cock bird of this species, 
who further differs from his browncapped mate by the pure ashy- 
grey of his upper plumage ; but notwithstanding the marked sexual 
difference in appearance, he shares with her the duty of incubation, 
and has been declared by more than one writer to sing while so 
employed—a statement that seems hardly credible. Closely allied 
to the Blackcap, which, it may be said, is a regular summer visit- 
ant, though examples have sometimes occurred in winter in England, 
are the so-called Garden-WARBLER, Sylvia salicaria (S. or Curruca 
hortensis of some authors), and the WHITE-THROAT. 
But the name Blackcap is also applied to some other birds, and 
both in this country and in North America especially to certain 
species of TITMOUSE and GULL which have the top of the head 
black, as well as locally to the SrONECHAT and Reed-BUNTING. 
BLACKCOCK, the male of the bird to which the name Grows 
or GROUSE seems to have been originally given. 
BLEATER, a name for the SNIPE, from the noise it makes in its 
love-flights, the cause of which has given rise to much discussion. 
BLIGHT-BIRD, see Zosterops. 
BLOOD is the fluid which circulates through the heart, arteries, 
and veins. It is mixed with lymph, its corpuscles being suspended 
in a fluid called blood-plasm. The arterial blood is of a lighter 
red than the venous, which is more purple blood. Blood shews 
the following composition :— 
1. Led blood-corpuscles, oval, flat disks, with rounded-off margins 
and a central nucleus which forms a slight swelling: they con- 
tain a substance known as hemoglobin, which, combining with the 
oxygen of the blood, causes the latter’s red colour. These red 
corpuscles are present even in a small drop of blood in innumerable 
numbers ; they are largest in the Cassowary, smallest in Humming- 
birds, their smallest axis measuring about mm. ;4+5 or 475, their 
larger axis from mm. +), to 735. 
2. Whute-blood or lymph-corpuscles ; by far less numerous, colour- 
less, and of very variable size (from mm. =}, to 7},), shewing lively 
amoeboid motions. 
3. The blood-plasm, consisting of fibrin and serum. The latter 
is a fluid, frequently yellowish, and is composed of water, albumen, 
and various salts. 
