286 PHYSIOLOGY CHAP. 



and to a minor degree of soaps. This well-established fact in our 

 opinion authorises the conjecture that, as the epithelium of the 

 stomach is impermeable to hydrochloric acid, so the intestinal 

 epithelium is impermeable to the fatty acids, which can thus be 

 absorbed only in the form of soaps, i.e. in the alkaline vehicle of 

 the pancreatic juice, bile, and succus entericus. 



Lombroso's observations on the reaction of the mucous 

 membrane stimulated by contact with fatty acids favours the 

 theory that fat is absorbed in the form of soaps. 



As shown above (p. 130), he saw that on introducing fatty 

 acids dissolved in bile into a Vella's loop, a copious secretion was 

 induced, and renewed as often as the secretion collected was 

 reintroduced, so long as it contained enough non-absorbed free 

 fatty acid. In view of the quantity of secretion discharged 

 altogether by the loop, and its potential alkalinity, we see that it 

 is approximately what is required to transform the whole of the 

 fatty acid into soap. 



Thus the fatty acid, even when completely dissolved, does 

 not appear to be absorbed as such : on the contrary, it evokes an 

 abundant intestinal secretion which tends to transform it into 

 soap. Soaps, however, are only present in very small quantities 

 in the faeces. How is it possible to interpret this phenomenon 

 otherwise than by assuming that the soaps have been absorbed, 

 and thus disappear from the secretion, while the fatty acid is 

 present because the intestinal epithelium refuses to absorb it, 

 probably by a kind of negative selection. 



VI. The problem of Protein Absorption is no less complex. 

 In the first place, a question presents itself which it will be well 

 to solve as a preliminary. Is peptonisation, or the more or less 

 advanced hydrolytic cleavage of proteins, necessary to their 

 absorption ? Are the intestinal epithelia permeable only to 

 peptones and proteases, or to the natural proteins as well ? The 

 first view was sustained by Mulder (1858), and Meissner (1859), 

 and was adopted by many others, particularly by Hermann. 

 Starting from the notion that absorption is a process of diffusion, 

 they held the peptonisation by which proteins are transformed 

 from indiffusible into diffusible bodies to be indispensable for their 

 absorption. 



The first critics of this theory, which found much favour, were 

 Briicke (1859-69) and Diatonow (1867-68), who asserted that the 

 natural proteins in solution (colloidal) are with few exceptions 

 capable of traversing the wall of the intestine without altera- 

 tion by the proteolytic enzymes. Better experimental evidence 

 for this theory was brought forward by C. Voit and Bauer (1869). 

 In a living dog they introduced protein into an intestinal loop 

 (previously washed and isolated by ligatures), in the form of 

 solutions of myosin, syntonin, and egg-albumin, and found them to 



