INTERNAL EESTITUTIVE SECEETIONS 



29*7 



both in Italy and abroad : some authors (as Drago, 1900 ; Keuter, 

 1901 ; liina Monti, 1903) agreed with his conclusions. Many, 

 however, hold the opposite opinion (Bezzola, 1901 ; Arcangeli, 1905 ; 

 Demjanenko, 1909) ; so that on the whole the theory of absorption, 

 considered as an internal secretion, is not, however well established 

 physiologically, sanctioned by histological evidence, as is the case 

 for other secretions. 



ry 



Fie. '.'<'>. Villus of small intestine of fowl in a more advanced stage of absorption and internal 

 secretion. (P. Mingazzini.) Lettering as in previous figure. At the apex.J'of the villus the 

 internal secretion of absorbed substances has already taken place, so that the epithelial cells 

 are reduced to their minimal size. To the left, a sort of lobe projects, in which there is a 

 maximal accumulation of the granular substance secreted by the epithelia. The stroma or 

 adenoid tissue of the villus is compact below, and looser above, and swollen by the penetration 

 of chyle between its fibres. Here the nuclei appear to be farther apart than below. 



The fats secreted by the columnar epithelial cells must pass 

 from the labyrinthine spaces of the adenoid tissue of the villus 

 into the central lacteal, and the carbohydrates and proteins mainly 

 into the interior of the capillary network of the villus. The 

 mechanism of this penetration has not been cleared up by direct 

 experiment, and we can only reconstruct this important process 

 by analogy. 



In regard to the passage of fat from the labyrinthine spaces 

 to the interior of the central lacteal, we may assume that the 

 epithelioid cells which form the wall of the latter leave lacunae 



