ASSIMILATION 



59 



Excretory Organs. — This residue is not to be regarded 

 as a true excretion, except in so far as it may contain 

 cast-off cells from the wall of the canal. The faecal 



LGL 



\n2j ^m;fm*:mmm?mm&&&& 



Fig. 38.— Small section of the wall of the intestine showing three villi. In A, art- 

 tery, vein and lacteal with their branches are represented ; in B, artery, vein 

 and branches; in C, the lacteal only; Cap., Network of capillaries; M. ep., Ep- 

 ithelial membrane; Lac, Lacteals; In.\., Level of inner wall of intestine ; GL, 

 Gland; A., Artery; V., Vein; Tn.2., Outer wall of intestine; VI., Villi ; L. Gl., 

 Layer of glands (mucous layer); L.c, Layer of cells and muscle. (Diagram- 

 matic.) (From Fitz.) 



matter has never been truly a part of the body, for it is 

 made of those parts of the food which were undigested 

 or unfit for digestion. True excretion is effected through 

 the kidneys, the lungs and the sweat glands. 



The wastes of the body are principally carbon dioxide, 



