IRON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS. 191 
the less readily does it dissolve the iron salts, and when used 
upon tissues acid alcohols have a smaller capacity for extracting 
the iron salts the longer the reagents are allowed to act, for 
the liberation of the iron from its “ masked ” condition entails 
the neutralisation of the acid, a very gradual process. Asa 
result of this neutralisation the iron salts become less soluble 
and would pass back into the tissues, but the danger of this 
happening is minimised or altogether prevented by the 
property which the chromatin has of retaining the iron that 
is set free in itself by the acid alcohol. This is shown 
specially in the case of nitric acid alcohol, for when sections 
of vegetable tissues are allowed to lie for two weeks in a large 
quantity of the reagent, the nuclei at the end of that time give 
as intense a reaction for iron as they do at the end of two 
days. The result is due to the fact that the tenacity with 
which the chromatin holds the iron liberated in it counteracts 
the extractive capacity of the reagent. 
The results of the action of nitric and sulphuric acid alcohols 
differ from those obtained with Bunge’s fluid! in one important 
respect. The two former, whether they are used upon the 
tissues in mass or on sections of the same, leave the iron, on the 
whole, in the parts in which it is liberated ; but when sections 
of tissues are treated with hydrochloric acid alcohol, the iron 
is extracted as quickly as it is liberated, and consequently 
such preparations on treatment with ammonium sulphide give 
a feeble reaction for iron or none at all. This is most 
distinctly seen when the temperature is raised, and if the 
reagent is allowed to act for two or three days under these 
conditions, no iron, organic or inorganic, is left in the prepara- 
tions. When the tissues are in mass, on the other hand, the 
quantity of acid that penetrates the preparations is largely 
neutralised and extraction takes place very slowly, with the 
result that teased-out portions of such tissues give a marked 
reaction for iron, limited, as in preparations obtained with 
1 Bunge’s fluid, or hydrochloric acid alcohol, consists of ninety volumes of 
alcohol of 95 per cent. strength, and ten volumes of a 25 per cent. solution of 
hydrochloric acid. 
VoL. 38, PART 2.—NEW SER. N 
