366 



ABSORPTION 



tion have been discussed. It was shown there that albumoses, peptones, 

 peptids, and the amido-acids are derived from the proteids as digestion 

 products. It has, in the past, been assumed that peptone represents the 

 form most freely absorbed. No peptone has, however, been isolated from 

 the blood or lymph on the vascular side of the epithelial membrane. But 

 the same may be said with equal truth of the other cleavage products. The 

 present supposition is that the proteids are taken up by the epithelium and 

 synthesized into other and more complex forms before being discharged 

 into the blood; or that the digestion cleavages are further broken down in 



FIG. 283. A Small Portion of Medullary Substance from a Mesenteric Gland of the Ox. d, d, 

 Trabeculae; a, part of a cord of glandular substances from which all but a few of the lymph-cor- 

 puscles have been washed out to show its supporting meshwork of retiform tissue and its capillary 

 blood-vessels (which have been injected and are dark in the figure); b, b, lymph-sinus, of which 

 the retiform tissue is represented only at c, c. X 300. (Kolliker.) 



the liver into elimination forms, such as urea, ammonium carbonate, etc. 

 If the intestinal epithelium produces change in the proteid on its passage 

 through, then it is evident that absorption of proteids is more than mere 

 osmosis and filtration. This idea is further strengthened by the known 

 power of the intestines to absorb certain albumins, egg albumin for example, 

 which is non-diffusible and non-dialyzable. 



In animal foods, such as eggs, meat, etc., it is estimated that about 98 per 

 cent of the proteid is absorbed; whereas in vegetable foods, where the pro- 

 teid is often protected from the action of the digestive enzymes, there may 

 be 10 to 15 per cent loss. Analysis of the total lymph discharge of the thoracic 

 duct fails to show any increase of proteids during active digestion, from which 

 it is inferred that proteids pass by way of the liver. 



