328 HENRY A. MATTILL AND HELEN I. MATTILL 



free (Schirokauer) forming a loose combination with peptone, perhaps of 

 the nature of an albuminate. Hemoglobin, nucleic acids, and related com- 

 pounds, on the other hand, are probably not decomposed until after they 

 have left the stomach. 



The further course of iron has been followed histologically in the in- 

 testinal tract and in organs and tissues by means of a microchemical 

 test with ammonium sulphid (and heat), sometimes with the addition of 

 potassium ferrocyanid and HC1 ; only the loosely combined iron responds 

 readily to this test, the "organic" iron only after long standing under 

 ammonium sulphid or not at all (Quincke ; Matzner). While the mechan- 

 ism of absorption has not been completely outlined it appears that most 

 of the iron enters the system in the duodenum, either in soluble form in 

 the plasma or through the phagocytic action of leucocytes. In dogs pro- 

 vided with various intestinal fistulas it was. observed (Rabe) that 87 per 

 cent of the ingested (inorganic) iron was absorbed before reaching the 

 ileum and a large percentage in the duodenum; but such a study of the 

 absorption of iron is complicated by the fact that iron is also largely 

 excreted by the intestine; this was shown as early as 1852 by Bidder and 

 Schmidt (a). They found it in all stages of fasting and later work on 

 fasting (Lehmann, Miiller, et aZ.), as well as the experiments of Forster and 

 Voit(a) showed that iron was constantly eliminated by the intestinal tract, 

 whether iron-containing food was ingested or not. The length of time 

 elapsing between the ingestion of a given amount of iron and its gradual 

 elimination extending over a period of days or even weeks (Gottlieb (a), 

 Hamburger), clearly indicated its absorption and also its excretion. 

 Direct experiments on isolated loops of the intestine were even more final 

 in this regard (Kobert and Koch; Honigmann). 



The fact that iron in process of excretion cannot be demonstrated mi- 

 crochemically the reaction is never obtained in fasting animals (Tarta- 

 kowsky(a)) and disappears in guinea pigs after 24 hours of fasting 

 (Swirski) suggests that all the iron demonstrable by this test is on its 

 way to absorption. This reaction is regularly obtained in the duodenal 

 epithelium and in the submucosa of the ascending colon; it is seldom 

 obtained in the gastric mucosa (Hochhaus and Quincke; Hari(a)) or in 

 the lower small intestine except in cases of abundant iron feeding 

 (Macallum(a)) or delayed absorption (Cloetta). Nor was Abderhalden 

 able to find any essential difference in manner of absorption between or- 

 ganic and inorganic iron in animals on a vegetable or meat diet and a 

 more recent investigation by means of the microchemical method (Hueck) 

 has confirmed these statements. Because of the gradual elimination of 

 iron the usual balance experiment of short duration (Stockman and Greig) 

 no matter how accurate, cannot afford far-reaching data on the metabo- 

 lism of iron. 



The intestinal elimination of iron takes place through the epithelium 



