Magendie on Absorption. 293 



sible. The absorption would be more rapid in proportion 

 as the vessels became more numerous, and their size di- 

 minished, because the absorbing surfaces would become 

 more extensive. 



This action of the membranes once acknowledged, nothing 

 can be easier than to comprehend how absorbed substances 

 are transported towards the heart, since they are constantly 

 drawn forward by the current which exists in the interior of 

 even the smoothest vessels. 



I was so much the more willing to admit this supposition 

 as I well remembered that, on poisoning an animal by pierc- 

 ing its thigh with a Java dart, all the softer parts which sur- 

 rounded the wound, to the distance of several lines, turned 

 to a brownish yellow colour, and assumed the bitter savour 

 of the poison. 



But a supposition which best connects a certain number 

 of phenomena, is, at bottom, but a more convenient manner 

 of expressing them ; and only assumes the character of a 

 theory after being confirmed by direct experiments, suffi- 

 ciently varied to leave no room to doubt. 



It therefore became necessary to continue my research- 

 es in order to determine at what point my supposition would 

 become inadmissible. 



The affinity of the vascular membrane for the substances 

 absorbed, being supposed to be the cause, or, at least, one 

 of the causes of absorption, this effect ought to take place as 

 well after the death as during the life of the animal. This 

 fact could be easily verified, for the vessels of a certain size ; 

 it is true that, taking into consideration their diameter, their 

 thickness and their smaller extent of surface compared with 

 the capacity of the canal, the experiment should present but 

 a feeble though still appreciable absorption. 



I took therefore one end of the jugular vein of a dog. 

 which, in an extent of more than three centimeters (about 

 one and a quarter English inches) did not receive any 

 branch, and stripped it entirely of its surrounding cellular 

 substance ; I attached a glass tube to each extremity, by 

 which means I established a current of warm water in its 

 interior ; I then plunged the vein in a slightly acidulated li- 

 quid, and carefully collected the liquid of the interior current. 



From this disposition of the apparatus it is evident that 

 no communication could exist between the interior current 

 and the exterior acidulated liquid. 



