THE BLOOD 193 



4th. Basophil leucocytes, practically absent from normal 

 blood, with a lobated nucleus and granules in the protoplasm, 

 staining with 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- 

 logical conditions. 



These various forms have certain properties (a) Amoeboid 

 movement. They can, under suitable conditions, 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 (pseudopodia), 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 con- 

 ditions, creep out of the blood vessels and wander into the 

 tissues (Diapedesis). 



(6) Phagocyte action. The finely granular leucocytes and 

 the lymphocytes have further the power of taking foreign 

 matter into their interior, and of thus digesting it. By this 

 devouring action, useless and effete tissues are removed and 

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

 In disposing of these micro-organisms the large granular cor- 

 puscles seem also to play an important part. This scavenger 

 action of the leucocytes is of vast importance in pathology. 



Chemistry of Leucocytes. The nucleus is chiefly made up 

 of nuclein, and in the protoplasm a nucleo-albumin, along 

 with two globulins and a small amount of an albumin, are 

 found. Along with these proteid substances glycogen and a 

 small amount of fat are present, while the chief inorganic 

 constituents are potassium salts. 



2. Blood Platelets. These are small circular or oval dis- 

 coid bodies, about one-third the diameter of a red blood cor- 

 puscle. 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 

 blood or to any rough point in the lining of the heart or 



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