CHAPTER XI 



THE CHANGES OF BLOOD IN THE ORGANS. INTERNAL 



SECRETION 



FROM what has been said in the foregoing chapters, it 

 follows that the blood streaming through an organ is changed 

 not only in respect to its gases but that it must undergo 

 other changes as well. In the organs in which the physio- 

 logical combustion takes place, e.g. in the muscles, the 

 blood supplies the material for this combustion and acquires, 

 besides the carbon dioxide, other products of combustion, 

 especially those containing nitrogen. In the glands the 

 blood loses substances from which the secretions are formed ; 

 in the walls of the intestine it takes up the absorbed foods ; 

 in the liver and in the adipose tissue it either deposits the 

 carbohydrates and fats or, if necessary, takes them up. 

 Moreover, the 'blood as a tissue (see page 52) has its own 

 metabolism, by which it is chemically changed. The above- 

 mentioned changes in the blood have, in some cases, been 

 demonstrated. But in most cases a difference cannot be 

 detected, because the amount of the substance given up or 

 acquired by the blood in flowing through an organ is so 

 small in proportion to the amount of blood flowing to and 

 from that organ that it lies within the limits of error of 

 observation. 



Besides the changes in the blood which we can under- 

 stand from the known physiological properties of the organ, 

 it undergoes still other changes, concerning the nature and 

 significance of which very little is known. Many organs 

 appear either to alter deleterious substances found in the 



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