SPECIAL PATHOLOGY. 



CHAPTER III. 

 DISEASES OF THE BLOOD. 



PLETHORA. 



THE condition of plethora, by which is understood an excess 

 of blood in the body, was regarded by the older writers as of 

 great importance, and most serious consequences were at- 

 tributed to it. Clinically, its presence was supposed to be 

 indicated by redness of the face and a vigorous circulation 

 occurring in high livers. 



Experimental evidence goes to show that if the amount of 

 blood in the vessels is artificially increased the result is but 

 temporary, as the excess is carried off by the kidneys in a few 

 hours. 



OLIGEMIA. 



The term oligemia indicates a diminution in the total quan- 

 tity of blood. This undoubtedly does occur after profuse 

 hemorrhages, severe vomiting, and diarrhoea. There is rea- 

 son to believe it exists in starvation and certain cachectic 

 conditions. 



QUALITATIVE CHANGES IN THE BLOOD. 



Alterations in the plasma: The amount of fibrin formed 

 from the blood was carefully investigated in the days of 

 frequent venesection. It is greatly increased in certain acute 

 inflammations, as pneumonia, pleurisy, and peritonitis. In 

 some infectious diseases, as typhoid and smallpox, the amount 

 of fibrin is not increased ; though if a pneumonia or pleurisy 

 occurs as a complication such an increase is immediately 

 noted. A reduction of the fibrin-forming property of the 

 blood has been occasionally observed, as in purpura and 



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