484 VETERINARY PHYSIOLOGY 



like the last, but large granules in the protoplasm which 

 stain deeply with acid stains. From 1 to 4 per cent, of the 

 leucocytes are of this variety (fig. 197, e). 



Basophil leucocytes are practically absent from normal 

 blood. They have a lobated nucleus and granules in the 

 protoplasm staining Avith basic stains. 



Myelocytes are large leucocytes with a large circular or 

 oval nucleus and a finely granular protoplasm. They are 

 not normal constituents of the blood, but appear when the 

 activity of the bone-marrow is increased in certain patho- 

 log^ical conditions. 



The leucocytes show — 



(a) Amoeboid movement- — Under suitable conditions they 

 undergo changes in shape, as may be readily seen in the 

 blood of the frog or other cold-blooded animal. The motion 

 may consist simply of the pushing out and withdrawal of 

 one or more processes (pseudojDodia), or, after a process is 

 extended, the whole corpuscle may follow it and thus change 

 its place, or the corpuscle may simply retract itself into a 

 spherical mass. As a result of these movements the 

 corpuscles, in certain conditions, creep out of the capillary 

 blood-vessels between the endothelial cells and wander into 

 the tissues (diapeclesis). The amoeboid movement is best 

 marked in the polymorpho-nuclear leucocytes. 



(b) Phagocyte Action. — The finely granular leucocytes 

 and the lymphocytes have further the power of taking 

 foreign matter into their interior, and of digesting it. By 

 this devourinoj action useless and effete tissues are removed 

 and dead micro-organisms in the body are taken up and got 

 rid of. This scavenger action of the leucocytes is of vast 

 importance in pathology. 



2. Blood Platelets. 

 These are small circular or oval discoid bodies about 

 one-third the diameter of a red blood corpuscle. Some 

 observers have stated that they contain a central nucleus. 

 They are very sticky and mass together when blood is shed 

 and adhere to a thread passed through the blood or to any 

 rough point in the lining of the heart or vessels. They 



