CHAP. VII.] THE VASCULAK SYSTEM. 77 



larger, the cell body becoming correspondingly smaller, until 

 finally the whole cell passes over into the process, thus moving 

 forward. These amoeboid movements are always very slow, 

 and are greatly influenced by the temperature, density, and 

 amount of oxygen in the fluid in which the cells lie. By virtue 

 of this locomotive power the white blood cells perform certain 

 evolutions within the blood-vessels ; they escape through their 

 walls, and sometimes singly, sometimes in vast numbers, move 

 through the lymph spaces in the surrounding tissues. This is 

 spoken of as the " migration of the white corpuscles." In an 

 "inflamed area" large numbers of white corpuscles are thus 

 drained away from the blood. These migrating corpuscles, or 

 wander cells, may, by following the devious tracks of the lymph, 

 find their way back into the blood; some of them, however, 

 may remain and undergo various changes. Thus in inflamed 

 areas, when suppuration follows inflammation, the white cor- 

 puscles which have migrated may become " pus corpuscles." 



Again, by virtue of their amoeboid movements, the white 

 corpuscles can creep around objects, enveloping them with their 

 own substance, and so putting them inside themselves. As an 

 illustration of this action of the white corpuscle, we may state 

 that, according to some observers in certain diseases in which 

 micro-organisms make their appearance in the blood, the white 

 corpuscles take up these organisms into their substance and 

 probably exert an influence over them, which modifies the 

 course of the disease of which these organisms are the essen- 

 tial cause. 



Furthermore, the white corpuscles are not only capable of 

 taking up particles in the blood, but are also capable of giving 

 up modified products to the blood, and it follows that these 

 metabolic changes must necessarily affect the composition of the 

 fluid plasma in which they lie. 



The plasma of the blood. The plasma is a clear, slightly 

 yellowish coloured fluid, consisting for the most part of water, 

 holding in solution or suspension proteid substances, fats, 

 various extractives, and saline matters. 



The proteid substances are albumin, para-globulin, and fibrin- 

 ogen. The albumin and para-globulin occur in about equal 

 quantities; but the fibrinogen, though a most important element 

 in the blood, occurs in very small quantities. The fats are 



