28 A MANUAL OF PHYSIOLOGY 



hand, the addition of water renders the corpuscles spheri- 

 cal ; more of the light passes through them, less is reflected, 

 and the colour becomes dark crimson (Plate I.). 



The White Blood-corpuscles, or Leucocytes. The red cor- 

 puscles are peculiar to blood. The white corpuscles may 

 be looked upon as peripatetic portions of the mesoblast (see 

 Chap. XIV.), and some of them ought not in strictness to be 

 called blood-corpuscles. They are more truly body cor- 

 puscles. Similar cells are found in many situations, and 

 wander everywhere in the spaces of the connective tissue. 

 They pass into the bloodvessels with the lymph, and may 

 pass out of them again in virtue of their amoeboid power. 

 They consist of undifferentiated living substance or ' proto- 



.A. ^ O . ^ /" r\ 



FIG. 2. AMOEBOID MOVEMENT. 

 A, B, C, D, successive changes in the form of an amoeba. 



plasm,' and under the microscope appear as granular, 

 colourless, transparent bodies, spherical in form when at 

 rest, and containing a nucleus, often tri- or multi-lobed. 

 Many of the leucocytes of frog's blood at the ordinary 

 temperature, and of mammalian blood when artificially 

 heated on the warm stage, may be seen to undergo slow 

 changes of form. Processes called pseudopodia are pushed 

 out at one portion of the surface, retracted at another, and 

 thus the corpuscle gradually moves or ' flows ' from place to 

 place, and envelops or eats up substances, such as grains of 

 carmine, which come in its way. This kind of motion was 

 first observed in the amoeba, and is therefore called amoeboid. 

 The leucocytes of human blood are not all of the same size, 



