THE ABSORPTION OF THE FOOD-STUFFS 133 



after eating a number of raw eggs the albumin may be 

 found in the urine. It evidently reaches the capillaries to 

 some extent before it can be hydrolyzed by the digestive 

 enzymes, even at a time when these are presumably pres- 

 ent and active. The application of mild poisons to the 

 lining of the intestine causes it to behave much more like 

 the typical indifferent membrane. Thus a weak solution 

 of sodium fluorid (which does not visibly disorganize the 

 cells) wipes out the selective properties which have been 

 instanced. This makes it seem the more probable that 

 the normal processes require the application of energy, and 

 that accordingly they cannot continue after the death of 

 the cells. 



A mosaic surface formed of cells, each one of which is a 

 living body, is far from comparable with a homogeneous 

 partition. Even if we leave out of account the crevices 

 between the cells which may bear a part in absorption, as 

 already noted, we must consider the individual cell to be 

 an elaborate structure. Its surface layer is undoubtedly 

 different in its chemical nature from its interior. There is 

 good reason to believe that the exposed border differs 

 entirely from the end which abuts on the connective tissue. 

 A result of this complex organization is the existence of a 

 property that might be called "polarity," that is, a capacity 

 to act in one direction rather than the other. A somewhat 

 ponderous expression for the same idea is found in the 

 phrase "irreciprocal permeability." This means special- 

 ization for absorption, and strongly suggests that if the 

 cells could be reversed in their relation to the interior of the 

 intestine they would begin to absorb from the lymph and 

 secrete into the canal. Gland-cells may be said to have 

 irreciprocal permeability in this reversed sense. 



The departure of the intestinal lining from the behavior 

 of a common membrane is still more obvious when we note 

 that absorption may be accompanied by chemical trans- 

 formation. The food-stuffs which leave the interior of the 

 canal do not of necessity reappear in the circulation in the 

 same form. Two possibilities exist: either the process of 



