266 THE HUMAN BODY 



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

 may be retracted and others thrust out ; and so the corpuscle goes 

 on changing its shape. These slow amoeboid movements are greatly 

 promoted by keeping the specimen of blood at the temperature 

 of the Body. By thrusting out a process 

 on one side, then drawing the rest of its 

 body up to it, and "tlren- sending out a 

 process again on the same side, the corpus- 

 cle- can .sjowty change its. place and creep 

 across trie field of the microscope. Inside 

 the blood-vessels these corpuscles often ex- 



FIG. 99 .A white blood- ecu te similar movements; and they some- 

 corpuscle sketched at sue- . . . . 

 cessive intervals of a few times bore right through the capillary walls 



seconds to illustrate the ... . 



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

 creep about among the other tissues. This 



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- 

 ing into themselves foreign particles present in the blood; this 

 they do in a manner similar to that in which an amosba feeds: 

 the process is known as phagocytosis and the cells exhibiting it as 

 phagocytes. Among the substances observed to be taken up by 

 white corpuscles are the minute organisms known as Bacteria, 

 certain species of which have been proved to be the causes of some 

 diseases. The white corpuscles doubtless in this way play an 

 important part in the cure of such diseases, or in their preven- 

 tion in persons exposed to infection. The accumulation of white 

 corpuscles in inflamed or injured parts is probably primarily as- 

 sociatecl with the removal of dead and broken-down tissues, 

 though it may be carried to excess as in the case of purulent ac- 

 cumulations. 



The Blood-Plates. These are a third kind of corpuscle which 



remained undiscovered for a long time after the others were known 



because they break up and disappear very soon after the blood 



is shed unless special precautions are taken to preserve them. 



*They are smaller than the red corpuscles; in structure and com- 



