294 PHYSIOLOGY CHAP. 



they are fitted to repair the losses that continually occur in the 

 individual cells. 



This does not, however, exclude the absorption of protein, as 

 such, more particularly of peptone, i.e. before the latter breaks 

 up into amino-acids. In fact, after herbivora (rabbits, guinea- 

 pigs) had been kept for some time on a milk diet, Hamburger 

 observed the presence of the so-called precipitine in the blood 

 (the " biological " reaction'). M. Ascoli, Vigano, and Moreschi 

 employed the same method to determine the fate of the ali- 

 mentary proteins. It is based on the property by which blood 

 serum is able to precipitate foreign proteins, against which it has 

 been immunised by repeated subcutaneous injections. Kaw egg- 

 white or roast chicken was fed to dogs, by means of the sound, the 

 reaction of the blood and lymph (from a thoracic fistula) to rabbit- 

 serum, previously immunised to these proteins, being tested before 

 and after they were introduced (the proteins being precipitated by 

 the serum). In consequence of this diet the lymph (less constantly 

 the blood) of the animal experimented on, was thrown out by 

 serum which had been immunised to the proteins fed. From this 

 Ascoli concluded that the highly complex atomic groups derived 

 from the proteins (if not the proteins themselves, unaltered) which 

 cause the biological reaction of precipitation, are able to pass 

 through the gastro-intestinal wall and penetrate to the lymphatic 

 system, without previous reduction to crystallisable products. 



VII. From all that has been said of the absorption of the 

 different groups of food-stuffs in the gastro-intestinal canal, and the 

 chemical changes that some of the absorbed products of digestion 

 undergo in consequence of the activity of the epithelial cells, it 

 is clear that the mechanism of these marvellous processes is 

 not essentially different from, certainly not less complex than, 

 that by which each living cell or independent elementary organism 

 draws the alimentary principles required for its nutrition and 

 development from the environment in which it lives, and then gives 

 off the products of its anabolic and katabolic activity. 



The special organ of intestinal absorption is the villus, which 

 in view of the complex of epithelial cells with which it is clothed, 

 may be regarded as an extraflected glandular crypt, in which the 

 epithelia do not absorb the lymph from the end which is attached 

 to the basement membrane, but take up the food-stuffs (whether 

 modified or not by the digestive process) from their free end, at 

 the striated border. The absorbed materials which are partially 

 modified by the metabolic activity of the cells are not poured 

 outwards as in the intraflected crypts, but are emptied into the 

 lymph sinuses of the adenoid tissue of the villi, whence they make 

 their way by the blood capillaries through the portal vein to the 

 liver, or by the central lymphatic, which leads to the thoracic duct. 



P. Mingazzini (1900) gave new support from the histological 



