126 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



In the body it may be said that well-nigh all the vital func- 

 tions are dependent upon osmosis. There are fluids separ- 

 ated by animal membranes everywhere. In the alimentary 

 canal, for instance, is a fluid containing matters fit to be ab- 

 sorbed; ramifying in the wall of that canal are blood and 

 lymph capillaries filled with fluid ; while separating the two 

 is an animal membrane consisting of the alimentary epithe- 

 lium, a little connective tissue and the endothelial lining of 

 the capillaries. These are conditions most favorable for os- 

 mosis, but the osmotic laws of the laboratory are by no means 

 immutable in the body. 



From what has been said of osmosis in general, and con- 

 sidering variations due to conditions of circulation, etc., the 

 following facts seem clear as to absorption in the body : ( i ) 

 The substance must be in a liquid or gaseous state; (2) it 

 must be diffusible; (3) the membrane must be permeable; 



(4) the greater current is toward the more dense solution 



(5) the less dense the solution the more quickly will it be ab- 

 sorbed; (6) the greater the pressure in the vessels the less 

 rapidly will absorption into them take place; (7) absorption 

 is more rapid the more rapid the blood current (continually 

 preventing "saturation" of the adjacent blood) ; (8) the 

 higher the temperature the more rapid is absorption; (9) 

 the "vital condition" of the cells is the most important fac- 

 tor of all. 



A thorough grasp of these principles and probabilities will 

 do much to clarify almost all the phenomena of vital activity, 

 and many questions of a pathological nature. 



Absorption from the Alimentary Canal. 



It has been said that all digested materials must find their 

 way into the blood. It is to be remembered that there are 

 two ways by which they reach the vascular circulation ; first, 

 by direct absorption into the capillaries of this system, and 

 second, indirectly, by absorption into the lymphatic circula- 



