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CHAPTEB III. 



CHANGES WHICH THE BLOOD UNDERGOES IN 

 DISEASE. 



INTRODUCTION. 



THE blood may be looked upon as the internal medium whither 

 tends the stream of matter which flows from the external world 

 into the organism, and whence simpler combinations of matter, 

 which are the result of the chemical processes of the organism, leave 

 it to form again a part of the external medium. The blood 

 represents a common reservoir which is continually being drawn 

 upon by each tissue and organ for the materials which it needs, and 

 to which, in its turn, each tissue and organ contributes its quota of 

 useful manufactured products or of useless waste. 



If we except the coloured corpuscles, whose function it is to act as 

 the internal oxygen-carriers of the body, and the colourless corpuscles, 

 which we have good reason to think are the precursors of the 

 coloured, the blood represents a solution of organic and inorganic 

 matters, which is continually being added to and taken from, in 

 different ways and degrees, by the different tissues and organs, and at 

 varying rates by each tissue or organ according to the degree of 

 its functional activity. 



The ancients looked upon the blood as essentially representing 

 vitality : as that part of the matter of the body in which specially 

 resided the life, and hence arose the natural wish to connect all the 

 morbid processes of the body, processes tending towards death, with a 

 perversion of the life-giving or actually vital liquid a wish which 

 found expression in the various phases of the humoral pathology 

 which under one form or another reigned more or less imperiously 

 over medicine until the fifth decade of the present century had 

 passed. 



If, however, we look upon the blood very much as a fluid con- 

 tained in a reservoir which is contributed to by many sources, and 

 whence at many points, by a variety of chemical and physical 

 processes, matter is being continuously removed, we shall, naturally, be 

 forced to admit that any changes which the blood undergoes are, in all 



