OF THE CIRCULATORY SYSTEM. SECT. XXIH. 6. 



which evince that the blood in the veins, and the 

 lymph and chyle in the lacteals and lymphatics, are 

 carried on by a fimilar force; otherwife the ftream, 

 which was propelled with a lefs power, could not 

 enter the veflels, which contained the ftream pro- 

 pelled with a greater power. From whence it ap- 

 pears, that the veins are a fyftem of veflels abforbing 

 blood, as the lacteals and lymphatics are a fyftem 

 of veflels abforbing chyle and lymph. See Section 

 XXVI. i. 



VI. The movements of their adapted fluids in the 

 various veflels of the body are carried forwards by 

 the actions of thofe veflels in confequence of two 

 kinds of ftimulus, one of which may be compared to 

 a pleafurable fenfationor defire inducing the veflel to 

 feize, and, as it were, to fwallow the particles thus 

 felected from the blood ; as is done by the mouths of 

 the various glands, veins, and other abforbents, 

 which may be called glandular appetency. The 

 other kind of flimulus may be compared to difa- 

 greeable fenfation or averfion, as when the heart has 

 received the blood, and is ftimulated by it to pufh it 

 forwards into the arteries ; the fame again ftimulates 

 the arteries to contract, and carry forwards the blood 

 to their extremities, the glands and capillaries. Thus 

 the mefenteric veins abforb the blood from the intef- 

 tines by glandular appetency, and carry it forward 

 to the vena portarum ; which acting as an artery 

 contracts itfelf by difagreeable flimulus, and pufhes 

 it to its ramified extremities, the various glands, 

 which conftitute the liver. 



It ieems probable, that at the beginning of the 

 formation of thefe veflels in the embryon, an agree- 

 able fenfation was in reality felt by the glands during 

 fecretion, as is now felt in the act of fwallowing pa- 

 latable food ; and that a difagreeable fenfation was 

 originally felt by the heart from the diftention occa- 



fioned 



