EXTRACT XV1II.B. 



EXCRETION. 



IT may be said, in its widest sense, that excretion repre- 

 sents the return, into the " outer world," of the residual 

 products of the raw materials of the food and drink 

 taken into the body, of the unutilised type solid and 

 liquid, of the solid, and liquid results of waste and 

 disintegration, and of the gaseous elements, or results, 

 of chemical interchange, which have not entered into, 

 or which have been released from, solid and liquid, 

 combination, or association. Typically its forms consist 

 of the alvine, the renal, the cutaneous and the pulmonary, 

 and they may be grouped around two great nerve 

 areas and two great lymph systems, viz. the sympathetic, 

 and the systemic nervous systems, and the haemal, and 

 neural lymph systems, respectively. The kidneys may 

 be said to excrete, mainly, from the sympathetic nervous 

 system, or area, the residual haemal lymph ; the skin, 

 in like manner, the peripheral systemic, and the sympa- 

 thetic, neural lymph that of the systemic motor area 

 finding its way into the haemal excepted and the bowel, 

 an admixture of both systems ; while the lungs give off, 

 the great proportion of the effete gaseous material, the 

 skin and bowel, also contributing. It will be seen, from 

 this division of excretory labour, that the hypo- and meso- 

 dermal areas, with a division of the ectodermal, are dealt 

 with by the kidneys and bowel, while that of the systemic 

 sensory area, together with part of the outer haemal, 

 is accomplished by the sweat agencies of the skin, the 



