IRON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS. 183 
by placing at the dry side of the cover-glass a drop of a mix- 
ture of one part of dilute glycerine and two of ammonium 
hydrogen sulphide, the drop so placed running under the cover, 
after which the preparation is replaced in the warm oven and 
in the end usually proves successful. I have found that when 
the isolated cellular elements are not very numerous and 
uniformly distributed under the cover-glass, evaporation rarely 
goes so far as to rendera resort to this remedy necessary ; but 
when the tissues are only partially teased, and fragments tilt 
or elevate the cover-glass, the mixture concentrates, the pre- 
paration dries at one side, and the sulphide is largely converted 
into polysulphide. 
The solutions of ammonia used in the preparation of the 
reagents were chemically pure, and in this respect, as well as 
in the cleanliness of the slides and covers, I paid due regard to 
the suspicion that there possibly exists a ferrous sulpho-hydrate 
(FeS,H,), soluble to a certain extent in solutions of ammonium 
hydrogen sulphide, the presence of which in the glycerine and 
sulphide mixture of my preparations might, through its diffu- 
sion into the nuclei and precipitation therein as ferrous sulphide 
(FeS), give confusing results. That no such compound existed 
in my reagents was shown repeatedly by allowing mixtures of 
the sulphide and glycerine to stand for weeks, when all the 
ammonium hydrogen sulphide was converted into the diammo- 
nium salt, or into polysulphides of ammonium, in the presence 
of which it would appear that the supposed existence of ferrous 
sulpho-hydrate is impossible. In these experiments no iron was 
found, nor did the mixtures in the end lose any of their trans- 
parency,—a result which tells against the possibility of any such 
iron compound existing in the mixtures employed upon teased- 
out cells. ‘The cover-glasses and slides were cleaned in solu- 
tions of hydrochloric acid to remove any adherent compounds 
of iron, and afterwards passed through distilled water and 
alcohol. The bottles in which the solutions of ammonium 
hydrogen sulphide were kept were also, first of all, cleansed 
in the same way. 
Nothing was gained by making ‘‘stock”’ mixtures, in the 
