CHAP. VIII.] THE VASCULAR SYSTEM. 



97 



an inch (0.008 mm.) in diameter, and about one-fourth that 

 in thickness. When viewed singly by transmitted light the 

 coloured corpuscles do 

 not appear red, but 

 merely of a reddish-yel- 

 low tinge, or yellowish- 

 green in venous blood. 

 It is only when the light 

 shines upon a number 

 of corpuscles that a dis- 

 tinct red colour is pro- 

 duced. When blood is 

 drawn from the vessels, 

 the red disks sink in 

 the plasma : they have 

 a singular tendency to 

 run together, and to 

 cohere by their broad FlG . 77 ._R ED AND WmT E CORPUSCLES OF 



Surfaces, SO as to form THE BLOOD. Magnified. A, moderately magnified, 



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



Cylindrical Columns like white corpuscles ; B, C, D, red corpuscles, highly 



piles Or rouleaux of ma S n ifi e d, seen in different positions ; E, a red cor- 

 puscle swollen into a sphere by imbibition of water ; 



Coins, and the piles join F, G, white corpuscles, highly magnified ; K, white 



thpmpWp tno-PtViPv in cor P uscle treated with acetic acid; H, I, red cor- 



1 puscles wrinkled or crenated. 



an irregular network. 



Generally the corpuscles separate on a slight impulse, and may 



then unite again. 



Each red corpuscle is composed of an external colourless 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 

 water the haemoglobin is dissolved out of the corpuscle, and 

 the colourless envelope remains as a faint circular outline. On 

 the other hand, the addition of salt to a preparation of blood by 



1 Haemoglobin is a compound proteid, i.e. its molecules consist of a proteid 

 portion, and of a pigment portion, the latter containing one atom of iron. 



H 



