IRON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS. 199 
that none of the iron found in the nuclei is derived from the 
cytoplasm, for there is very little and often no cytoplasm in 
the cells of the coats of the ovules in this plant, and yet the 
nuclei of these give as intense a reaction as those of the ovary 
of Erythronium, Iris, Hyacinthus, or any form in which 
the cytoplasm is abundant. 
In order to get the best results with the use of the acid 
alcohols, I have found that the tissues must be well hardened. 
If the tissues are fresh or imperfectly hardened, the application 
of acid alcohols for a time sets free the organic iron, but the 
structure of the cellular elements is more or less changed in 
such cases by the acids—a change not at all found to occur 
when the tissues have been carefully hardened. Strong alcohol 
(90—95 per cent.) was used for this purpose, and it was found 
to present, over the other hardening reagents, a number of 
advantages. It can by redistillation be made free from iron, 
and when it is of absolute strength it neither extracts any of 
the iron compounds (hzmatins excepted) from tissues, nor 
allows these to diffuse. There is the important point also, that 
tissues fixed with it can be subjected to all the reactions for 
iron, without incurring the risk of complications due to the 
deposition of iron or other metallic salts, which occur when 
other hardening reagents are used. In this way one may treat 
pieces of a tissue with ammonium hydrogen sulphide and with 
the acid alcohols, and thus allow the methodsto control each other, 
When, on the other hand, it was not necessary to use ammo- 
nium hydrogen sulphide on the tissues, other hardening reagents 
were employed, but only such as did not, by their presence in 
the tissues, interfere with or obscure the demonstration of the 
iron. Saturated solutions of corrosive sublimate and } per 
used advantageously, parts of the fresh plant are thrown into boiling distilled 
water, and those which remain uncoloured at the end of ten minutes are 
further hardened for several days in absolute alcohol. I have often treated 
material so prepared with the warm glycerine and sulphide mixture for from 
four to ten days, and then with an acid ferrocyanide solution converted the 
ferrous sulphide demonstrated into Prussian blue. Such preparations are pro- 
bably the most instructive obtainable in regard to the question of the relation 
of iron to the vegetable cell. 
