BLOOD AND LYMPH. 83 



their form and place. While, when in a state of 

 rest, they assume in general the spheroidal form, as 

 above stated, 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 gradually larger and 

 larger, the cell-body becoming correspondingly 

 smaller, until finally the whole cell seems to have 

 passed over into the process, thus moving forward. 

 Sometimes processes are thrown out and again with- 

 drawn, and not infrequently the whole cell flattens 

 out into an irregular-shaped mass, so thin as to be al- 

 most invisible. Not infrequently clear rounded spaces, 

 called vacuoles, suddenly appear in the cell-body dur- 

 ing its movements, and either remain for some time, 

 or soon' disappear as suddenly as they came. 



These movements are called amceboid movements ; 

 they are always very slow, and are greatly influenced 

 by the temperature, density, and oxygen-content of 

 the fluid in which they lie. By virtue of this loco- 

 motive power the white blood-cells perform certain 

 evolutions within the vessels ; they escape through 

 their walls, and. sometimes singly, sometimes in vast 

 numbers, move through the tissues in the larger and 

 smaller lymph-spaces. This emigration of white 

 blood-cells occurs apparently, to a slight extent, 

 under normal conditions ; but it is under patho- 

 logical conditions that it is most active. 



