132 



THE BLOOD 



circumference. The ameboid movement which can be demonstrated in 

 human colorless blood corpuscles can be most conveniently studied in the 

 newt's blood. Processes are sent out from the corpuscle. These may be 

 withdrawn, but more often the protoplasm of the whole corpuscle flows 

 gradually forward to the position occupied by the process, thus the corpuscle 

 changes its position. The change of position of the corpuscle can also take 

 place by a flowing movement of the whole mass, and in this case the loco- 

 motion is comparatively rapid. The activity both in the processes of change 



FIG. 117. Human Colorless Blood Corpuscle, showing its successive changes of outline 

 within ten minutes when kept moist on a warm stage. (Schofield.) 



of shape and also of change in position is much more marked in some cor- 

 puscles than in others. Klein states that in the newt's blood the changes 

 are especially noticeable in a variety of the colorless corpuscle, w r hich consists 

 of a mass of finely granular protoplasm with jagged outline and contains 

 three or four nuclei, or in large irregular masses of protoplasm containing 

 from five to twenty nuclei. 



The property which the colorless corpuscles possess of passing through 

 the walls of the blood vessels will be described later on. 



FIG. 118. Blood Plates, showing chromatic centers regarded by some as nuclei, and ex- 

 hibiting ameboid movement. (Schafer^ from Kopsch.) 



The Blood Plates or Thrombocytes. A third variety of corpuscle 

 found in the blood is known as the blood plates. They are circular or elliptical 

 in shape, of nearly homogeneous structure, and vary in size from 0.5 to 5^. 

 Hence they are smaller than the red corpuscles. They vary in number from 

 5,000 to 45,000 per cubic millimeter and are preserved by drawing fresh 

 blood directly into Hayem's or other preserving fluid. Chemically, they 



