STRUCTURE AND FUNCTIONS OF BLOOD AND LYMPH 301 



have been thought to aid the circulation of blood through it. It 

 also becomes congested during the period of digestion. Whether 

 this is important or merely incidental is not known. 



The Colorless Blood-Corpuscles or Leucocytes (Fig. 97, F, 

 H, G). The colorless or white corpuscles of the blood are far less 

 numerous than the red ; in health there is on the average about one 

 white to three hundred red, but the proportion may vary con- 

 siderably. Each is finely granular and consists of a soft mass of 

 protoplasm enveloped in no definite cell-wall, but containing a 

 nucleus. The granules in the protoplasm commonly hide the 

 nucleus in a fresh corpuscle, but dilute acetic acid dissolves most 

 of them and brings the nucleus into view. These colorless cor- 

 puscles belong to the group of undifferentiated tissues, and differ 

 in no important recognizable character from the cells which make 

 up the whole very young Human Body, nor indeed from such a 

 unicellular animal as an Amoeba. They have the power of slowly 

 changing their form spontaneously. At one moment a leucocyte 

 will be seen as a spheroidal mass; a few seconds later (Fig. 98) 

 processes will be seen radiating from this, and soon after these 

 processes may be retracted and others thrust out; and so the cor- 

 puscle goes on changing its shape. These slow amoeboid movements 

 are greatly promoted by keeping the specimen of blood at the tem- 

 perature of the Body. By thrusting out a 

 process on one side, then drawing the rest of 

 its body up to it, and then sending out a 

 process again on the same side, the corpus- 

 cle can slowly change its place and creep 

 across the field of the microscope. Inside 

 the blood-vessels these corpuscles often ex- 



. ., , ,, FIG. 98. Awhiteblood- 



ecute similar movements; and they some- corpuscle sketched at sue- 

 times bore right through the capillary walls ^M**.' 

 and, getting out into the lymph-spaces, changes of form due to its 



2, rnu- amoeboid movements. 



creep about among the other tissues. Ihis 



migration is especially frequent in inflamed parts, and the pus 

 or ''matter" which collects in abscesses is largely made up of 

 white blood-corpuscles which have in this way got out of the 

 blood-vessels. The average diameter of the white corpuscles is 

 one-third greater than that of the red. 



The colorless corpuscles, or some of them, are capable of tak- 



