416 ABSORPTION. 



The process by which digested materials are taken into 

 the blood is called absorption. It is now recognized that two 

 sets of vessels are concerned in the performance of this func- 

 tion ; namely, the blood-vessels and the lacteals. Those parts 

 of the food which have been rendered fluid and are capable 

 of forming a homogeneous mixture with the blood-plasma 

 are absorbed chiefly by the blood-vessels, though a small 

 portion finds its way into the lacteals. The emulsified fats 

 are taken up in greatest part by the lacteals, though a small 

 quantity is taken directly into the blood. In treating of 

 this subject, it will be convenient to consider the action of 

 these two kinds of vessels separately. 



Absorption ty Blood - Vessels. 



That soluble substances can pass through the delicate 

 walls of the capillaries and small veins and that absorption 

 actually takes place in great part by blood-vessels is a fact 

 which hardly demands discussion at the present day. There 

 are now all the proofs that could be asked in support of 

 this view. Soluble principles which have disappeared from 

 the alimentary canal have been repeatedly found in the blood 

 coming from the part, even when the lymphatics have been 

 divided and communication existed only through the blood- 

 vessels. The old theoretical view which was entertained be- 

 fore the lymphatics and lacteals were discovered was that 

 absorption took place by blood-vessels ; but after special ab- 

 sorbent vessels were described, it was generally supposed 

 that they furnished the only avenue for the entrance of new 

 matters into the economy, though the doctrine of vascular 

 absorption was retained by a few. 1 It was only after the 



1 The observations of William and John Hunter, who attempted to show by 

 experiments upon living animals that the lacteals were the only absorbent ves- 

 sels of the intestines, have been so completely disproved by more recent investi- 

 gations that they do not demand extended discussion. These experimenters 

 showed that milk introduced into the intestinal cavity was absorbed by the lac- 

 teals and not by the veins ; but the evidence that absorption of other fluids did 

 not take place by the veins was entirely insufficient. The experiments referred 



