PHYSICAL NECESSITY OF VASCULAR ABSORPTION. 103 



discharge of this function. The term venous absorption, employed to 

 express it, is perhaps somewhat incorrect, since there is no reason that a 

 venous capillary should have any advantage over an arterial one in this 

 respect. The rapidity with which substances in a state of solution are 

 taken up from these cavities has been well demonstrated by such in- 

 stances as those of the detection of the ferrocyanide of potassium in the 

 urine within 2 J minutes of its having been deposited in the stomach, or 

 by the death of dogs in a similar short period after strong alcohol had 

 been administered to them, their blood being found to be charged with 

 that combustible substance. 



Among substances thus finding their way into the circulation by di- 

 rect vascular absorption may be enumerated such soluble salts as have 

 little affinity for the tissues, mineral and organic acids, alcohol, ether, 

 volatile oils, vegetable alkaloids, and coloring matters, as those of rhu- 

 barb, madder, gamboge. 



In fact, if there were not these physiological considerations, we should 

 have to admit absorption by the blood-vessels as a mat- Absorption by 

 ter of physical necessity ; for, under the circumstances of the Wood-ves- 



. /^r . i ' t -i se ^ s occurs as a 



theirsituation, they must take up soluble matters presented physical neces- 

 to them. Through the pores of their delicate structure sub- sit - y - 

 stances in the liquid state will pass to mingle with the blood. 



Though we have treated of respiratoiy or lacteal absorption as specif- 

 ically distinct from absorption by the blood-vessels, the circumstances 

 here alluded to evidently point out that the resulting action of the villi 

 of the intestines is of a mixed kind ; for, though the epithelial cells and 

 the commencing pouch of the lacteal may exert a definite influence, the 

 network of blood-vessels which lies immediately beneath the epithelium 

 must be engaged in precisely the same manner as the network of blood- 

 vessels between the gastric follicles. The permeation of the walls of 

 these tubes by substances in a state of solution is dependent, as we are 

 now to see, upon a purely physical principle, which is just as applicable 

 in the one case as it is in the other. The leading solid ingredients of 

 the chyle being fat and albumen, the former is perhaps introduced by the 

 proper lacteal structure, and the latter, taken up by the vascular network, 

 exudes in part again from it into the lacteal arrangement. 



In the case of absorption, as in that of respiration, hereafter to be de- 

 scribed, there is a physical principle in operation which it is necessaiy 

 to understand. I shall proceed to explain it on this occasion as far as is 

 needful for the present purpose, and complete the description in the chap- 

 ter on the function of respiration. The peculiar views here set forth, 

 so far as they differ from those ordinarily expressed, I believe to be 

 warranted by my own experiments elsewhere published. 



The absorbent action of the blood-vessels depends on the force known 



