Chap, hi.] .ELIMINATION OF WASTE PRODUCTS. 523 



the system. Thus various minerals, alkaloids, salts, pigmentary 

 and odoriferous matters, may be passed unchanged. Many sub- 

 stances thus occasionally taken undergo, however, changes in 

 passing through the body ; the most important of these, since 

 the changes which they undergo throw light on the metabolic 

 processes of the body, will be considered in a succeeding chapter. 



