v^ 



•^ I 



100 ELEMENTARY PHYSIOLOGY less. 



shape of prisms. The h<i;nioglobin of human blood 

 crystallises with ditHciilty, but that of the guinea-pig, rat, 

 or dog, much more readily. 



3. The White Corpuscles.— The colourless corpuscles 

 (Fig. 'M, a a, F.) are larger than the red corpuscles, their 

 average diameter being 10/x (05^5 of an inch). They are 

 further seen, at a glance, to ditfer from the red corpuscles 

 by tlie irregularity of their form, and by their greater 

 stickiness or adhesiveness, shown by theii* tendency to 

 attach themselves to the glass slide, while the red 

 corpuscles float about and tumble freely over one another. 



A feature of many of the colourless corpuscles, even 

 more remarkable th in tlie irregularity of their form is the 

 unceasing variation of shape which they exhibit so long as 



Fid. 33. — Successive Forms assi'mkd by Colourless Corpuscles of 

 Human Blood. (Magnified about 600 diameters ) 



The intervals between the forms a, b, c, d, was a minute ; between d 

 and e two minutes ; so that the whole series of changes from a to e took 

 five minutes. 



they are alive. The form of a red corpuscle is changed 

 only by influences from without, such as pressure, or the 

 like ; that of most colourless corpuscles is undergoing 

 constant alteration, as the result of changes taking place 

 in their own substance. To see these changes well, a 

 microscope with a magnifying power of live or six hvindred 

 diameters is requisite, and some arrangement for keeping 

 the preparation gently warmed (to 40' C), since heat 

 makes the movements more active ; and, even then, they 

 are so gradual that the best way to ascertain their exist- 

 ence is to make a drawing of a given colourless corpuscle 

 at intervals of a minute or two. This is what has been 

 done with the coi'puscle represented in Fig. 33, in which 



