114 1'insiOLOGY OF THE CIKCT LATION. 



different parts, both as to its decree, and also as to 

 the nature of the particular forces constituting it. 



Thus in the lungs, the weight of the atmosphere 

 is the only force that can act on the exterior of those 

 minute blood-vessels through which absorption is 

 known to occur with extreme rapidity ; whereas the 

 whole contents of the abdomen are, in addition to 

 being subjected to the action of the ordinary causes 

 of external pressure, forcibly compressed by the 

 diaphragm and abdominal muscles. By the con- 

 tractions of the alimentary canal, the nutritious 

 matters are, moreover, forced against the walls of 

 the blood-vessels ramifying upon the intestinal coats. 



This latter fact viz., that in that particular part 

 of the body where the absorption of food is effected, 

 there exists throughout the animated creation an 



O 



express contrivance for increasing the pressure acting 

 on the exterior of the blood-vessels does appear 

 to me to constitute a very powerful argument in 

 support of this view of the nature of the absorbing- 

 process. And when, in the treatment of disease, a 

 more active absorption is desirable, experience has 

 shown that there is no more effectual mode of 

 accomplishing this object than by increasing the 

 external pressure in the affected part. It is, of 

 course, requisite that the external force applied 

 should never exceed a moderate amount ; otherwise 

 the circulation through the part, and with it all 

 absorption, would be totally arrested ; whereas a 

 more gentle support not only facilitates absorption 

 directly, by forcing the surrounding fluids into the 

 interior of the blood-vessels, but, by diminishing 



