THE CIRCULATORY OR VASCULAR SYSTEM 137 



undergoes a chemic action with the air through the 

 medium of the blood ferment, fibrinogen, which glu- 

 tinates the corpuscles with the other constituents to form 

 the clot. This ferment does not exist as such in the blood 

 when contained in the blood-vessels, but is supposed to be 

 the result of the destruction of the white corpuscles and 

 the blood platelets. Some authors assume that these 

 platelets contain a nuclein body, coupled with proteids, 

 which is the essential factor in the coagulation of the 

 blood. It is thought that these structures disintegrate 

 very rapidly when blood is drawn from the body, liberat- 

 ing the ferment, and so producing coagulation. 



Changes in Blood in Disease. The blood undergoes 

 various changes in disease. Traces of organic com- 

 pounds, viz., uric acid, urea, keratin, keratinin, taurin, 

 cholesterin, and leucin, may also occur in the blood, and 

 cause serious, if not fatal, derangement. 



There may occur variations in the relative proportion 

 of its constituents; for instance, in plethora the red cor- 

 puscles are said to be increased in number, while in anemia 

 they are deficient in number or quantity. After the 

 loss of great numbers of the red blood-corpuscles they are 

 slowly reproduced, hence the long-continued pallor after 

 hemorrhages. The fibrin is increased in acute inflam- 

 mation, especially in those of the serous membranes, in 

 acute rheumatism, pneumonia, erysipelas, phthisis, ton- 

 sillitis, and inflammation of the lymphatic vessels. It 

 is always in excess in the pregnant female. On the other 

 hand, it is always diminished in enteric fever, cerebral 

 hemorrhage and congestion, in scurvy, and after profuse 

 hemorrhages. The albumen increases in Bright's disease 

 and glandular inflammation, erysipelas, scarlet fever, and 

 tuberculosis. The salts of the serum are diminished in 

 enteric fever and cholera. Mixture with foreign substances 

 from the inhalation of noxious gases may occur, or the 



