1 6 A MANUAL OF PHYSIOLOGY 



Envelope and spongework are sometimes spoken of as the 

 stroma of the corpuscle, in contradistinction to its most impor- 

 tant constituent, a highly complex pigment, the haemoglobin, 

 which, not in solution as such, but either in solution as a com- 

 pound with some other unknown substance, or more probably 

 bound in some solid or semi-solid combination to the stroma, 

 fills up the space within the envelope in the interstices of the 

 spongework. Since there is good reason to believe that the 

 haemoglobin as obtained artificially from the corpuscles is not quite 

 the same substance as the native blood-pigment within them, the 

 latter is sometimes distinguished by a separate name haemo- 

 chrome. To the physical properties of the stroma it is usual 

 to attribute the great elasticity of the corpuscles that is, the 

 power of recovering their original shape after distortion for 

 their elasticity is no wise impaired by the removal of the haemo- 

 globin. 



Rouleaux Formation. When blood with disc-shaped corpuscles 

 is shed, there is a great tendency for the corpuscles to run together 

 into groups resembling rouleaux, or piles of coin. No satisfactory 

 explanation of this curious fact has yet been given. 



Crenation of the corpuscles, a condition in which they become 

 studded with fine projections, is caused by the addition of moderately 

 strong salt solution, by the passage of shocks of electricity at high 

 potential, as from a Ley den jar, or by simple exposure to the air. 

 Concentrated saline solutions, which abstract water from the cor- 

 puscles and cause them to shrink, make the colour of blood a brighter 

 red, because more light is now reflected from the crumpled surfaces. 

 On the other hand, the addition of water renders the corpuscles 

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

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



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 mesoderm (see 

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

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

 Similar cells are found in many situations, and wander every- 

 where 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 protoplasm, 

 less differentiated than that of any other cells in the body, 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, 



