48 THE HUMAN BODY. 



commonty hide the nucleus in a fresh corpuscle, but dilute 

 acetic acid dissolves most of them and brings the nucleus into 

 view. These pale corpuscles belong to the group of undiffer- 

 entiated 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 pale corpuscle will 

 be seen as a spheroidal mass; a few seconds later (Fig. 15) 

 processes will be seen radiating from this, and soon after 

 these processes may be retracted and 

 ot hers 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 

 FIG. 15. -A white blood- the rest of its body up to it, and then 

 \ e nterfais e of a a s few sending out a process again on the same 

 fW^dS VIS side, the corpuscle can slowly change its 

 movements. I^QQ and creep across the field of the 

 microscope. Inside the blood-vessels these corpuscles often 

 execute similar movements; and they sometimes bore right 

 through the capillary walls 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 

 whiue 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 

 taking into themselves foreign particles present in the blood; 

 this they do in a manner similar to that in which an amoeba 

 feeds: the process is known as phagocytosis and the cells ex- 

 hibiting 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 (zymotic diseases). The 

 white corpuscles may in this way play an important part in 

 the cure of such diseases, or in their prevention in persons 

 exposed to infection. The accumulation of white corpus- 

 cles in inflamed or injured parts is probably primarily as- 



