[RON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS. 179 
condition contains iron, or contains it only after death, deriving 
it by absorption from the blood or other surrounding fluids, 
or even out of the reagents themselves, if these are not 
absolutely free from iron. In his remarks upon my methods 
he states that Bunge’s fluid, upon which I relied to extract the 
iron of inorganic and albuminate combinations from sections 
of tissues, does not take away the iron artificially combined 
with dead nuclein even after six days. 
Hammarsten! has isolated from the pancreas of the ox 
an iron-holding nucleo-proteid containing 4°48 per cent. of 
phosphorus. 
II. Metuops or Srtupy. 
In my first communication on the method of demonstrating 
micro-chemically the occurence of ‘‘ masked” iron, the reagent 
whose use I described was called, in a general way, ammonium 
sulphide, This is a term that is properly applicable only to the 
diammonium compound represented by the formula (NH,),S, 
but it is sometimes given to solutions which contain either 
ammonium hydrogen sulphide (NH,HS), or polysulphides of 
ammonium, or to mixtures of diammonium sulphide and 
ammonium hydrogen sulphide. At the time I was unable to 
determine which of the two latter is the most effective as a 
reagent in liberating the iron from the chromatin, since 
either, when recently prepared, gave, with cellular elements 
from the same piece of tissue, reactions in which differences in 
intensity were not noticeable, and, while uncertain upon this 
point, I felt justified in adopting the generic term “ ammonium 
sulphide” to designate a reagent which might be held to 
indicate either of the two compounds. 
About two years ago I gave further attention to the question 
whether one form of the reagent is more efficient than the other 
in this respect, and the results of a series of experiments made 
since then have led me to the conclusion that ammonium 
1 “Zur Kenntniss der Nucleo-proteide,” ‘Zeit. fiir Physiol. Chemie,’ vol. 
xix, 1894, p. 19. 
