76 ANATOMY FOE NURSES. [CHAP. VIL 



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 

 absorbing the water causes the corpuscles to shrink, and become 

 wrinkled or crenated. The red corpuscles are practically small 

 flattened bags, or sacs, the form of which may be changed by 

 altering the density of the plasma. They are very soft, flexible, 

 and elastic, so that they readily squeeze through apertures and 

 passages narrower than their own diameters, and immediately 

 resume their proper shape. 



Function of the red corpuscles. The red corpuscles, by virtue 

 of their haemoglobin, are emphatically oxygen carriers. Ex- 

 posed to the air in the lungs, the haemoglobin combines with 

 the oxygen present in the air; this oxygen the haemoglobin 

 carries to the tissues ; these, more greedy of oxygen than itself, 

 rob it of its charge, and the reduced haemoglobin hurries back 

 to the lungs for a fresh supply. The colour of the blood is 

 dependent upon this combination of the haemoglobin with oxy- 

 gen ; when the haemoglobin has its full complement of oxygen, 

 the blood has a bright red hue ; when the amount is reduced, it 

 changes to a dark purplish hue. The scarlet blood is usually 

 found in the arteries, and is called arterial; the dark purple 

 in the veins, and is called venous blood. 



White corpuscles of the blood. The white, colourless corpus- 

 cles, or leucocytes, are few in number compared with the red, 

 and both on this account, and because of their want of colour, 

 they are not at first easily recognized in a microscopic prepara- 

 tion of blood. Their form is very various, but when the blood 

 is first drawn they are rounded or spheroidal. Measured in this 

 condition they are about ^Q-Q- of an inch in diameter. The 

 white corpuscle may be taken as the type of a free animal cell. 

 It is a small piece of protoplasm, containing one or more nuclei, 

 and has no limiting membrane or cell-wall (vide Fig. 61 F. G.). 



These corpuscles, or cells, possess the power of spontaneous 

 movement, and are capable of changing their form and place. 

 While, when in a state of rest, they assume in general the 

 spheroidal form, we find that when they become active they 

 send out variously shaped processes, some fine and delicate, 

 others broad, and of very irregular shape. We often see, after 

 a process has been thrown out, that it becomes larger and 



