BLOOD SYSTEM. 



351 



to fresh blood it prevents coagulation, and the globules 

 will settle to the bottom. If freshly drawn blood be 

 stirred or whipped with a bundle of twigs or wires, the 

 whole of the fibrin coagulates on the wires or twigs as 

 fleshy strings, and may be withdrawn. The defibrinated 

 blood will no longer coagulate. This is important, be- 

 cause it is necessary sometimes to transfuse the blood 

 of one person into the veins of another, or even the 

 blood of an animal into the veins of a man. If so, 

 then the blood so transfused must not be liable to 

 coagulation. 



Functions of the Blood. — 1. Plasma. — The plasma 

 may be regarded as essentially the finished result of 

 albuminoid food, although it contains in small quantities 

 many other substances for use or for elimination by ex- 

 cretory organs. It is essentially the peptones, sangui- 

 ned, vitalized, and ready for use. Its fundamental 

 function, then, is tissue building — i. e., repair and growth 

 of tissue. Its peculiar property of easy change from 

 liquid to solid form is eminently adapted for this pur- 

 pose. Its liquid condition is necessary for circulation ; 

 its solid condition is necessary for making tissue. Fur- 

 ther than this, however, the whole process of assimila- 

 tion, or change from blood to tissue, is still enveloped in 

 mystery. 



2. Red Globules. — The function of these is better un- 

 derstood than any other part of the blood. They are 

 undoubtedly carriers of oxygen from the air to the tis- 

 sues for combustion of their waste. This it does by vir- 

 tue of the property of haemoglobin, already mentioned. 

 This substance takes oxygen from the air in respiration, 

 becomes oxidized as oxyhemoglobin, is carried to the 

 tissues, and there gives up its oxygen for the combus- 

 tion of waste. It is easily seen, therefore, why an abun- 

 dance of red globules is necessary for health and vigor. 

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