ABSORPTION. 199 



passing through the epithelial layer, come at once in contact with the 

 vascular network. The extension of absorbing surface, from the division 

 and inosculation of these vessels, and the renovation of their fluids by 

 the movement of the circulation, provide for their constant activity, 

 and drain away the absorbed fluids from the interior of the villus as 

 fast as they are taken up by its surface. 



The activity of the blood-vessels in this process is a matter of direct 

 observation. It was first shown by Magendie,* who found that the 

 absorption of poisonous substances would take place, in the living ani- 

 mal, both from the cavity of the intestine and from the tissues of the 

 leg, notwithstanding that all communication through the lacteals and 

 lymphatics was cut off, and the blood-vessels alone remained. These 

 results were corroborated by Panizza, who succeeded in detecting the 

 substances absorbed in the venous blood returning from the part. This 

 observer, after having opened the abdomen of a horse, drew out a fold 

 of the small intestine, about 20 centimetres in length, which he included 

 between two ligatures. A ligature was then placed upon the mesenteric 



FIG. 41. 



CAPILLARY BLOOD-VESSELS OF THE INTESTINAL YILLI; from the Mouse. (Kolliker.) 



vein receiving the blood from this portion of intestine ; and, in order 

 that the circulation might not be interrupted, an opening was made in 

 the vein behind the ligature, so that the blood brought by the mesen- 

 teric artery, after circulating in the intestinal capillaries, passed out 

 at the opening, and was collected for examination. Hydrocyanic acid 

 was then introduced into the intestine, and almost immediately after- 

 ward its presence was detected in the blood flowing from the venous 

 orifice. The animal, however, was not poisoned, since the acid was 

 prevented by the ligature from gaining an entrance into the general 

 circulation. 



Panizza afterward varied this experiment in the following manner : 

 Instead of tying the mesenteric vein, he simply compressed it. Hydro- 

 cyanic acid being then introduced into the intestine, no effect was pro- 

 duced so long as the vein remained compressed ; but as soon as the 



* Journal de Physiologic. Paris, 1825, tome i., p. 18. 



