INORGANIC FOODS. 391 



certain that a part of the absorbed iron is also conducted to the portal 

 vein of the liver. The latter organ forms one of the chief storage places 

 of iron salts. The spleen also absorbs considerable iron. It is probable 

 that the lymph carries some of the iron back to the intestines, and is 

 eliminated through the caecum and large intestine. Evidently the leuco- 

 cytes play an important part in the processes of taking up and trans- 

 porting the little particles of iron, for they are often observed laden with 

 iron particles, both in the paths of absorption and in those of elimination. 

 There is no doubt that a large portion of the iron introduced into the 

 organism is again eliminated through the intestines. It is at present 

 uncertain as to what parts of the intestines share in this elimination. 

 This is particularly true of the small intestine, which perhaps partici- 

 pates in both the absorption and elimination of iron. We must not 

 forget, above all, that microchemical reactions have a limited value. 

 They serve merely to give us a qualitative picture of the activity of 

 definite compounds, but never give us much idea as to the amounts of 

 substances entering reactions. Moreover, the method used in the above 

 experiments for detecting the presence of iron qualitatively was not 

 entirely satisfactory. We have already mentioned, for example, that 

 the iron in hematin does not react with the ordinary reagents used in 

 testing for the presence of iron, and that hematogen only gives a notice- 

 able reaction after the solution has stood for some time. It is easy to 

 conceive that the animal organism may contain its iron firmly bound in 

 other compounds besides hematin, so that in. any case the mere fact that 

 we do not detect the presence of iron by a qualitative test does not prove 

 that the tissue tested does not contain this element. On the other hand, 

 the fact that we do not get these iron tests in cases where other methods 

 (examination of the ash) show that it is actually present, does not give 

 any reliable information concerning the way that the iron is held in com- 

 bination. We have already seen that colloids play an important part in 

 the animal organism, and that they are apparently capable of preventing 

 certain reactions from taking place. Thus we found that the formation 

 of precipitates was often prevented, even in cases where the reaction had 

 actually taken place. The precipitate is not seen, merely because the 

 internal friction between the colloid particles prevents the tiny parts of 

 insoluble substance formed from uniting to cause a visible precipitate. 

 This point is all too frequently lost sight of in scientific work. In many 

 cases the statement that iron is present in a firm state of " organic " 

 combination is not justifiable. 



It is, we regret to say, at present impossible to follow with sufficient 

 accuracy the question of the absorption of iron and the distribution of 

 the absorbed iron among the separate organs. . The amounts of iron 

 absorbed are so small that with our present methods it is entirely out of 



