IRON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS, 201 
sublimate as a hardening reagent, which I have frequently 
used, it may be urged that it possibly assists in the diffusion 
through the tissues of the inorganic compounds of iron, and 
that consequently the distribution of the latter, in preparations 
thus hardened, may not correspond with that obtaining in the 
fresh tissue. Where this is not under investigation it is a 
matter of no importance, for treatment of sections of the tissue 
with warm Bunge’s fluid for a few hours removes such com- 
pounds, and the sections so treated may be subjected to the 
action of the various reagents described to demonstrate the 
organic iron; but when it is desired to study the distribution 
of both classes of iron compounds in a tissue, the objection 
urged would, if well founded, exclude corrosive sublimate as a 
hardening reagent for this purpose. My experiments in rela- 
tion to this were made on pieces of the same organ (liver and 
kidney of guinea-pig and of Amblystoma) hardened with 
alcohol alone, and with corrosive sublimate and alcohol, and I 
have found, on comparing the distribution of iron in both series 
of preparations, that though the possibility of the diffusion of 
iron salts is not excluded when corrosive sublimate is used, yet 
no appreciable evidence of it was manifestedin the preparations. 
I have not, however, based my observations in any one case 
alone upon material hardened in corrosive sublimate, but have 
used material hardened in alcohol in all cases to control the 
results obtained when that reagent was used. 
When the iron was liberated by acid alcohol the whole of 
it appeared as a ferric salt in some tissues, while in others a 
very small portion of it also was set free as a ferrous com- 
pound. The latter condition was illustrated in some of the 
Protozoa. Insuch preparations all the iron set free is demon- 
strated, after treatment with ammonium sulphide, as a ferrous 
salt, and the preparations may then, on being acted upon with 
a mixture of equal volumes of dilute solutions of hydrochloric 
acid and potassic ferrocyanide, reveal all their liberated iron 
as Prussian blue. The iron in the ferrous form is usually so 
very minute in quantity, if present at all, that it may be 
1 For an explanation of the preponderance of the ferric compound see p. 268. 
