CHAP. VII.] THE VASCULAR SYSTEM. 



of biconcave disks. 

 average size is 



Red corpuscles of the blood. The red corpuscles have a nearly 

 circular outline like a piece of coin, and most of them have a shal- 

 low, dimple-like depres- 

 sion on both sides ; their 

 shape is, therefore, that 

 The 

 of 



an inch in diameter, and 

 about one-fourth that 

 in thickness. When 

 viewed singly by trans- 

 mitted light the col- 

 oured corpuscles do not 

 appear red, but merely of 

 a reddish-yellow tinge, 

 or yellowish-green in 

 venous blood. It is only 



when the light shines FIG. 62. - RED AND WHITE CORPUSCLES OK 

 Upon a number of COr- THE BLOOD - Magnified. A, moderately magnified, 

 , , ... the red corpuscles are seen in rouleaux; a, a, 



pUSCleS that a distinct white corpuscles; B, C, D, red corpuscles, highly 

 red colour is produced. ma n i ne d seen m different positions ; E, a red cor- 

 puscle swollen into a sphere by imbibition of water; 

 F, G, white corpuscles, highly magnified ; K, white 



When blood is drawn 



from the vessels, the red cor P uscle treated with acetic acid ; * i> *i COP- 



puscles wrinkled or creuated. 



disks sink in the plasma: 



they have a singular tendency to run together, and to cohere 

 by their broad surfaces, so as to form cylindrical columns like 

 piles or rouleaux of coins, and the piles join themselves together 

 in an irregular network. Generally the corpuscles separate on 

 a slight impulse, and may then unite again. 



Each red corpuscle is composed of an external colour/ess enve- 

 lope with coloured fluid contents. Quain. 



The envelope is a very delicate membrane of a fatty nature, 

 and may be ruptured or dissolved under certain conditions. 

 The colour of the fluid contents is due to a crystallizable sub- 

 stance called haemoglobin. 1 If water be added to a preparation 

 of blood under the microscope, the water passes into the cor- 

 puscle, and the concave sides of the corpuscle become bulged 

 out so that it is rendered globular. By the further action of 



1 Haemoglobin is a proteid, and contains, in addition to the usual proteid 

 elements, a certain amount of iron. 



