IRON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS. 193 
in its original position in the cell has led me to try the effects 
of solutions in which the strength of the acid was less than 
1 per cent.,! and they have been found, when used upon thin 
sections of tissues, to give very successful preparations, permit- 
ting the iron liberated to be demonstrated as fully as after the 
employment of either sulphuric or nitric acid alcohol. 
The time during which these reagents must be allowed to 
act on a piece of tissue varies. I prefer to give general state- 
ments on this point, because specific directions are impossible 
in a case where the size of the object, the quantity of the 
reagent, and the temperature constitute the conditions. 
Bunge’s fluid extracts as readily as it liberates the iron in 
thin sections of tissue, but when the latter is in mass the 
reagent requires a length of time which may vary from a week 
to two months, all depending on the size of the object and on 
the temperature, which in summer may be that of the room 
(20°—29° C.), but in the colder seasons that of the warm oven 
(35° C.). Sulphuric acid alcohol acts more slowly, and con- 
sequently requires a longer time for liberating the iron in 
unsectioned objects, while in sections its action is complete in 
from one to four days, this depending also on the temperature, 
the most favourable being 35° C. A longer stay than is just 
sufficient to liberate all the organic iron results in removing 
from the sections some of the iron set free, the more being 
extracted the longer the sections lie in the reagent. When 
examples of the Protozoa and Protophyta were subjected to 
1 These differences in extractive capacity exhibited by weak and strong 
alcoholic solutions of hydrochloric acid have apparently not been noted by 
Petit (loc. cit.), who used the diluted reagent in a Soxhlet apparatus to 
remove the inorganic iron compounds from barley. As the boiling-point of 
hydrochloric acid is higher than that of alcohol, it is obvious that little of the 
former must pass from the 1 per cent. solution at the bottom of the flask as 
vapour to condense above and act on the substance whose iron is to be ex- 
tracted, while the alcohol is readily converted into vapour; in other words, 
the reagent in the upper part of the apparatus must be much more dilute than 
that in the flask below, and consequently its extractive power must be very 
feeble. This method is, therefore, open to the objection that it does not 
ensure the removal of inorganic iron compounds, 
