TRANSACTIONS OF SECTION I). 779 



tried, sulpliuvic acid and sulpliurous anhydride gave tlie best results, thougli manj' 

 other agents, especially saline solutions, produce tlie same effect. 



When nuclei, previously steeped for a certain time in these liquids, are treated 

 with ammonium sulphide their chromatic elements take a greenish-hlack colour, 

 while the action of an acidulated solution of potassium ferricyanide gives them an 

 intense blue colour, caused by the formation of Turnbull's blue. 



These reactions are strictly limited to the chromatic filaments or chromato- 

 somos of tlie nucleus, the protoplasm remaining absolutely colourless. In pre- 

 sence of such a perspicuous reaction, there cannot remain the slightest doubt about 

 the presence of iron in the nucleinic elements actually under observation. 



But a question now arises : Is Macallum right when he contends that ' the 

 chromatin of every cell, animal or vegetable, is an iron compound'? — that is to 

 say, a regular chemical combination "with fixed proportions. 



I have no peremptory objection to oppose to Macallum's conclusion. But, 

 though his experiments seem to have been carefully carried out, I must confess 1 

 am not entirely satisfied with the accuracy of his generalisation, and cannot help 

 thinking that the union of nuclein with iron might be a rather accidental com- 

 bination taking place after death only, and similar to that which it efl'ects with 

 many other substances, especially colouring matters. 



This suggestion is not a mere supposition; it proceeds from some observationa 

 I have made lately. 



I was able to ascertain that dead nuclein has a very strong afUnity for iron 

 compounds. The nuclei of freshly extracted cells, when steeped in a solution of 

 sulphate of iron, FeSO^, even as weak as 1 for 2,000 parts of water, take with 

 ammonium sulphide or potassium ferricyanide a much more intense coloura- 

 tion than they did before, when simply treated with sulphuric acid. A conse- 

 quence of that observation on dead nuclein is, that it is extremely ditlicult to 

 ascertain wliether living nuclein really contains iron, or whether it only absorbs it, 

 after it has been killed, out of the blood or other surrounding liquids, or even out 

 of the reagents themselves if they are not absolutely free from iron. Biologists 

 ought therefore to test their reagents very carefully before using them, and also 

 to take great care to avoid the contact of the slightest trace of organic or inorganic 

 iron with the cells. And that is not an easy task at all, for everyone knows that 

 this metal spoils everything, and is everywhere throughout nature. 



For my part, though my reagents were as pure as possible, I am not certain at 

 all, as far as the present, that the iron made visible in my preparations really 

 belonged to the living nuclein, and had not been absorbed after death only. 

 Macallum did not experimentally ascertain this affinity of nuclein for iron com- 

 pounds. I know, however, that he used to treat his objects with an acidulated 

 alcoholic mixture, called Bunge's fluid, a liquid which is supposed to take out, after 

 ten hours of action, all the organic and inorganic iron, excepting that combined 

 with nuclein. But I have observed that Bunge's liquid does not take away the 

 iron artificially combined with dead nuclein even after six days. 



I observed also that various iron compounds are attracted by nuclein, and 

 that its affinity is stronger for the ferrosum radical than for the ferricum. But 

 iron is not the only metal which nuclein can absorb and retain. I succeeded in 

 fixing in it manganese, nickel, and even copper, which all gave in the nucleus only 

 their usual reactions. Nickel is almost as strongly attracted as iron itself is. 

 Molybdenum also is retained by nuclein, and this last observation induces me to be 

 cautious about another method of micro-chemical technic recently published. Dr. 

 Lilienfeld, just a month ago, announced he had discovered a method of detecting 

 phosphorus in the nucleus, with the aid of ammonium molybdate and pyrogallol. I 

 suspect that the yellow-brown colouration he regards as characteristic of the 

 phosphorus is caused by the accumulation of ammonium molj'bdate in the nuclein ; 

 the brownish colouration that ammonium molybdate itself gives with pyrogallol is 

 darker in the nucleus, not because nuclein contains phosphorus, but because it 

 retains more of the ammonium molybdate than the protoplasm does. 



1 may add also that other substances found in the cell have a similar attrac- 

 tion for iron. Macallum pointed out that amyloid substances contain iron, and I 



