384 COLLOIDS IN BIOLOGY AND MEDICINE 



waters) are active only to the extent that they are dissolved in the 

 hydrochloric acid of the gastric juice. I cannot form any idea as to 

 the process of absorption since in the alkaline content of the small 

 intestine where absorption occurs, the iron is thrown down again 

 as a colloidal gel. Those colloidal iron preparations from which the 

 iron ion slowly splits off (e.g., liquor ferri albuminati, ferratin, etc.) are 

 preferable since they exert a less injurious effect on stomach and 

 intestine (indigestion and constipation) . After intravenous or subcu- 

 taneous injection of iron salts colloidal ferric albuminate compounds 

 are formed which may cause severe anaphylactic-like symptoms of 

 poisoning (see p. 382) . When iron salts are taken by mouth this action 

 does not occur, since the iron is arrested in the liver. The cathodal- 

 migrating positive iron oxid hydrosol precipitates with the anodal- 

 migrating blood colloids as an irreversible gel. This is the reason why 

 ferric chlorid is so suitable for hemostasis. The greater part of the Fe 

 in FeCl 3 exists as iron oxid hydrosol as the result of hydrolytic cleavage. 

 When blood coagulates, the excess of HC1 is bound by the blood salts. 



R. BUNSEN, in his first scientific paper, showed that " freshly pre- 

 cipitated ferric hydroxid" is able to take up considerable quantities 

 of arsenious acid and recommended it on this account as an antidote 

 for arsenic poisoning. W. BILTZ * 2 showed that the distribution of 

 arsenious acid between iron oxid hydrogel and water has the charac- 

 teristic of an adsorption curve and not that of a chemical combina- 

 tion. The protective action against arsenious acid depends moreover 

 upon the method of preparing the ferric oxid hydrogel. Works on 

 materia medica prescribe that it be freshly prepared. Perhaps, the 

 inhibiting action which, according to L. PINCUSSOHN,* ferric oxid 

 hydrosol exerts on pepsin digestion depends upon adsorption. 



Although colloidal ferric hydroxid serves as the typical positive 

 colloid H. W. FISCHER * 2 succeeded in preparing a negative ferric oxid 

 hydrosol, as well. He did this by pouring ferric chlorid solution into 

 sodium hydrate solution which contained glycerin as a protector. 

 Glycerin and the excess of alkali were then removed by diffusion. 

 Instead of glycerin other polyvalent alcohols, e.g., mannit, erythrit 

 and cane sugar, may be employed. The object of his experiments 

 was to obtain ferric oxid hydrosol which might be injected intrave- 

 nously. Positive ferric oxid' precipitates with the negative serum 

 colloids; on this account the intravenous injection of positive ferric 

 oxid is immediately fatal to animals, on account of embolism. A 

 remarkable exception to this was found by C. FOA and A. AGGAZZOTTI * 

 in dogs; they are insensitive to positive ferric oxid; no explanation 

 for this exists. Negative ferric oxid may be mixed with serum in any 

 proportion. It forms a deep ruby red solution which may at times 



