4T8 A MANUAL OF PHYSIOLOGY 



sodium chloride, are readily taken up, sulphates with difficulty. 

 Iron is absorbed by the bloodvessels, but also to some extent by 

 the lacteals. From the blood it is carried to various organs, 

 especially the spleen and liver. There is reason to believe that 

 the eosinophile leucocytes take some share in its transportation. 



It was supposed by Bunge that only organic compounds of 

 iron could be absorbed, and that the undoubted benefit derived 

 from the administration of inorganic iron compounds, such as 

 ferric chloride, in chlorosis, was due not to their direct absorption, 

 but to their shielding the organic compounds from the attack 

 of the sulphuretted hydrogen in the intestine (p. 396) . But this 

 theory has been shown to be inconsistent with the facts. For 

 instance, after the administration of salts of iron, the iron in 

 the blood, liver, spleen, and other organs increases, but there is 

 no accumulation of iron in the liver of an animal to which salts 

 of manganese have been given, although these are equally 

 decomposed by sulphuretted hydrogen. 



Absorption of Proteins. The proteins of the food or their 

 digested products also pass directly into the blood-capillaries 

 which feed the portal system. For it has been shown that after 

 ligature of the thoracic duct protein substances are still absorbed 

 from the intestine, and the urea corresponding to their nitrogen 

 appears in the urine. And the total nitrogen in the chyle 

 flowing from a fistula of the thoracic duct in a man was not found 

 to be increased during the digestion of protein food. The 

 quantity of chyle escaping in a given time was also unaffected, 

 whereas during the digestion of fats it was greatly augmented 

 (Munk). 



Although a certain amount of egg-albumin, serum-albumin, 

 alkali-albumin, and other native or slightly altered protein 

 substances can be absorbed as such by the small, and even by 

 the large, intestine, there is no evidence that, under ordinary 

 conditions, this mode of absorption is of any practical importance. 

 For when native proteins, with the possible exception of the serum 

 proteins from an animal of the same species, are introduced 

 ' parenterally ' that is, injected directly into the blood, the peri- 

 toneal cavity, or the muscles, or under the skin, so that they do not 

 reach the tissues by way of the alimentary canal they behave 

 in a very different manner from the same proteins when given 

 by the mouth. One notable difference is that the parenterally 

 administered proteins give rise in general to the formation of 

 specific precipitins (p. 30). This is not the case when they 

 are administered per os, unless, like raw egg-white, which, as 

 already mentioned (p. 375), evokes no secretion of gastric juice, 

 they remain long undigested in the alimentary canal, when an 

 amount sufficient to cause the production of precipitins may 



