THE ABSORPTION OF THE REDUCED FOODSTUFFS 



1031 



as much as 12 grams of fat being absorbed by a dog of medium weight 

 in the course of one hour. Histologically, it is of interest to note that 

 the fat globules may be traced in their journey through the epithelial 

 lining by virtue of the power of the unsaturated fatty acids to reduce 

 osmic acid. When stained in this way they appear as dark granules 

 of varying size within the cytoplasm of the different cells. It should 

 be remembered, however, that this stain does not furnish a means of 

 determining the actual amount of fat present within these cells, be- 

 cause only the free fatty acids are rendered visible thereby. On leav- 

 ing these cells the fat globules enter the tributaries of the lacteals. 1 

 There is no reason to believe that they are transported into these 

 channels by the leukocytes, as has 

 been supposed by Schafer and 

 others. The histological picture 

 just briefly described, has led many 

 observers to conclude that the fat 

 globules traverse the intestinal epi- 

 thelium in their original form. 

 This view constitutes the so-called 

 mechanistic theory of fat absorption. 

 As we have seen, the evidence now 

 at hand shows that the fat is broken 

 down and is reconstructed into 

 neutral fat before it leaves the lining 

 cells. This fact forms the basis of 

 the chemical theory of fat absorption. 

 The Absorption of the Proteins. 

 The proteins of the food are re- 

 tained in the small intestine in the 

 form of peptones and their amino- 

 acid derivatives. The latter trav- 

 erse the intestinal epithelium and 

 are eventually converted into the 

 proteins of the body. We know this to be true, because amino-acids 

 may be isolated from the blood, and because animals may be kept in 

 nitrogen-equilibrium by feeding them with completely predigested 

 protein mixtures. It has also been observed that the introduction 

 of foreign proteins and even of peptones into the circulation, gives 

 rise to severe symptoms and may even result in the death of the 

 animal. In other words, the direct introduction into the blood-stream 

 of substances which are otherwise chemically indistinguishable from 

 the digested proteins is usually followed by the development of anaphy- 

 lactic reactions. These same substances given by mouth, are per- 

 fectly harmless. It appears, therefore, that the proteins cannot be. 

 absorbed as such from the intestine, but must first be reduced into 



1 Whitehead, Am. Jour, of PhysioL, xxv, 1910, 28, and Mendel, ibid., xxiv, 

 1909, 493. 



FIG. 521. SECTION THROUGH THE 

 LINING CELLS OF THE INTESTINE (RAT) AT 

 DIFFERENT PERIODS AFTER THE INGESTION 

 OF FAT. 



