BLACKCOCK— BLOOD 43 



superfluous. Enougli to say that its tones always brought to his 

 mind the lines in As You Like It (Act ii. sc. 5) : 



" And turn his merry note 

 Unto the sweet bird's throat." 



The name, however, is only ai^plicable 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 Gurruca 

 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 Stonechat and Eeed-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-BIED, 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. Red 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 haemoglobin, 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. -y]^ or y^-g-, their 

 larger axis from mm. -^ to ^wr- 



2. White-hlood or lymph-coipuscles ; by far less numerous, colour- 

 less, and of very variable size (from mm. -g-i^ to ^-q), shewing lively 

 amoeboid motions. 



3. The hlood-plasm, consisting of fibrin and serum. The latter 

 is a fluid, frequently yellowish, and is composed of water, albumen, 

 and various salts. 



