308 Secretion and Excretion. [Book IX. 



teries opening on the furface of membranes, with- 

 out the intervention of glands. Fluids, which are 

 defigned for the lubrication of pafiages, are very ge- 

 nerally difcharged into fmall bags or follicles, whence 

 they are exprerTed, when their prefence is moft ne- 

 cefiary. 



Few of the fecreted fluids are difcharged from the 

 body exacbly in the ftate in which they were firft 

 prepared, but gradually become more vifcid or acrid j 

 fmce, while they remain in the receptacles deftined 

 for their prefervation, their more watery parts are 

 continually taken away by the action of the abfor- 

 bents. 



We have hitherto confidered fecretion to be on 

 every occafion the work of arteries, but it is now 

 necefiary. to take notice of a remarkable exception 

 to this rule, and to inform the reader, that the moft 

 copious fecretion in the body is performed by veins. 

 The blood, which is carried by the Arteries to the body 

 at large, is generally returned by the readied paflages 

 to the heartj but it is ordered other wife with refpect 

 to that which is lent to the bowels. 



The blood from the abdominal vifcera is re- 

 ceived by a large vein, furnifaed with remarkably 

 denfe coats, and called, from entering the liver as 

 through a gate, the vena portarum ; this vein is dif- 

 tributed through the fubftance of the liver, in the 

 fame manner as arteries are diftributed through other 

 glands. 



The liver, however, is furniflied with an artery 

 which may poffibly have fome influence in the prepa- 

 ration of the bile. The ramifications of this artery 

 inofculate with thofe of the vena portarum, and the 

 blood from both is returned together to the heart, by 

 veins which empty themfelves into the vena cava. 



A fad 



