CHAPTER IX 



THE OUTPUT OF WASTE MATTER 



65. IT has already been pointed out that the 

 activities of the living tissues cause to some 

 extent a breaking up of living matter, and the 

 appearance of waste products. In addition 

 to this, waste matters may arise from the 

 using up by the protoplasm in cells of matters 

 previously stored up in them. That is to 

 say, there may be intracellular chemical 

 changes excited by enzymes in stored matters, 

 as well as chemical changes involving the 

 protoplasm. Both of these varieties of chemi- 

 cal change may produce substances that are 

 of no further use in the body, and may even 

 be injurious if allowed to accumulate in the 

 blood. ' Such matters are not allowed to 

 accumulate : they are quickly removed so 

 that only small percentages are usually found 

 in the blood, and this fluid, as has already 

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