CHEMICAL COMPOSITION OF THE BLOOD 115 



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. 



The Blood Plates or Thrombocytes. A third variety of corpuscle 

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

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



FIG. 118. Blood Plates, Showing Chromatic Centers Regarded by some as Nuclei, and Ex- 

 hibiting Ameboid Movement. (Schafer, from Kopsch.) 



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 

 contain a nucleo-proteid, *and it is supposed that they take part in the phe- 

 nomenon of coagulation. According to Deetjen and others, ameboid move- 

 ment has been demonstrated in these bodies. 



CHEMICAL COMPOSITION OF THE BLOOD. 



In considering the chemical composition of the blood, it will be convenient 

 to take in order the composition of the various chief factors into which the 

 blood may be separated, viz., The Plasma ; The Serum ; The White Cor- 

 puscles ; The Red Corpuscles. 



The Composition of the Plasma. The plasma is the liquid part 

 of the blood in which the corpuscles float. 



It contains the fibrin factors, inasmuch as when drawn from the blood- 

 vessels it undergoes coagulation and splits up into fibrin and serum. It 

 differs from the serum in containing fibrinogen, but in appearance and in 

 reaction it closely resembles that fluid. Its alkalinity, however, is greater 

 than that of the serum obtained from it. It may be freed from corpuscles 

 by the centrifugal machine, or by the other means enumerated below. 



