XV THE CIRCULATORY SYSTEM 261 



removal of skeletal and muscular tissues is effected in large 

 part through the agency of the white corpuscles. 



The spindle cells, as their name implies, are spindle shaped, 

 but their general outline is subject to considerable variation. 

 They are from one-half to two-thirds the length, and from 

 one-third to one-half the breadth of the red cells. They 

 possess a certain power of amoeboid movement, especially in 

 the young state. The spindle cells, according to Neumann, 

 are developed from the small leucocytes, and during the 

 springtime acquire hemoglobin and become transformed 

 into red corpuscles. They are normal constituents of the 

 blood at all times of year and are usually colorless ; only in 

 the spring do they transform into red cells. Soon after the 

 blood is shed they run together into masses and play an 

 important role in producing the clot. 



The plasma, or fluid portion of the blood, is of very com- 

 plex constitution ; it contains fats, sugar, and numerous pro- 

 teids in solution, a considerable number of salts, various 

 products arising from the breaking down of tissues through- 

 out the body, several gases, chiefly oxygen, nitrogen, and 

 carbon dioxide, and many other substances not included in 

 any of the above classes. While all but a small part of the 

 oxygen is carried by the hemoglobin of the red blood cor- 

 puscles, the other materials of the blood are contained in a 

 state of solution in the plasma. Under certain conditions 

 the plasma coagulates, or gives rise to a solid substance 

 called fibrin, which, with the corpuscles which become 

 entangled in it, forms the clot. The remaining portion 

 of the plasma is called the serum. Clotting of blood is 

 brought about by means of contact with foreign bodies. 

 Powdered substances, filter paper, or any objects which 

 bring a large amount of surface in contact with the fluid 

 greatly facilitate the precipitation of fibrin. On the other 



