190 A. B. MACALLUM. 
ties hydrochloric acid may have in this respect are possessed, 
in a greater or less degree, by other mineral acids, whether in 
dilute aqueous solutions or in alcohol, and the results were of 
such a character as to induce me to employ these reagents on 
all species of cells in which the distribution of iron had been 
determined with ammonium hydrogen sulphide. 
The more serviceable of these were found to be sulphuric 
acid and nitric acid dissolved in alcohol of 95 per cent. 
strength. The former was prepared by adding four volumes 
of the strong acid to one hundred of alcohol, while the latter 
contained three volumes of the acid (of 1:4 sp. gr.) in one 
hundred of alcohol. 
The chemicals used in the preparation of these reagents 
were free from traces of iron, and care was taken to have all 
bottles and vessels used to hold them also free from adherent 
iron compounds. It was, of course, impossible to provide 
against the iron in the glass, but I am not certain that the 
reagents derived any from this source, even in infinitesimal 
quantities. The alcohol used contained not a trace of iron, 
During the last eighteen months re-distilled methylated spirit 
was found to be in every way as serviceable as the pure ethyl 
alcohol used earlier in the investigation. 
The alcohol of these reagents largely prevents the occurrence 
of digestive changes which the acids effect when, in aqueous 
solutions, they are allowed to act on tissues for several days, 
and especially at a slightly elevated temperature. Another 
important function of the alcohol is to prevent a too rapid 
extraction of the liberated iron, and thereby also its diffusion 
from one part of the tissue into another, from nucleus to cell, 
or from cell to nucleus. Acid alcohols dissolve iron salts 
more readily than does alcohol alone, but less so than aqueous 
solutions of the acids. For example, ferrous sulphate is 
insoluble in absolute alcohol and in strong methylated spirit, 
but it is soluble in these when they contain a small quantity 
of sulphuric acid,—not, however, in any way as much so as in 
distilled water, or in dilute aqueous solutions of sulphuric 
acid. The smaller the proportion of the acid in the alcohol 
