of the Presence of Iron in Chromatin. 279 



hoematin is as readily absorbed and as tenaciously held by chromatin 

 as are some dyes. Indeed, the accuracy of Zaleski's observations on 

 hepatin, the iron-holding miclein of the liver cells, may be open also 

 to objection on this score. Tt is, to a certain extent, accepted that 

 the liver is the organ which converts the haematin of disintegrated 

 haemoglobin into the bile and urine pigments. Now, the liver cells 

 are probably the agents in this conversion, and the haematin which is 

 held by them and their nuclei cannot, presumably, be removed by the 

 washing out of the lobular capillaries with saline solutions. 



Such being the difficulty, the solution appeared, at first sight, 

 to lie in the preparation of nuclein from an animal from which 

 haemoglobin is absent. No opportunity presented itself for making 

 such preparations of the substance in desired quantities, and it 

 appeared to me that nuclein from such a source could not be free 

 from the histo-haematins found by MacMunn to be present in all 

 tissues, except those of the nervous system. With this difficulty 

 before me, I felt compelled to relinquish that line of investigation, 

 and to attempt another. 



It occurred to me that it might be possible to demonstrate under . 

 the microscope the presence of iron in the chromatin of the cellular 

 elements of such tissues as are almost wholly free from haematins, 

 and in those tissues which are hardened so rapidly, as to prevent a 

 transference from without of haemoglobin or haematiu into the cells. 

 Such tissues are the cutaneous epithelium in Amphibia and Fishes, 

 the cornea and cartilage in all Vertebrates. This demonstration I 

 had often attempted without success, and I was forced to adopt the 

 conclusion that, if iron is present in the intact nucleus, it is either 

 so firmly bound in the molecules of chromatin that the ordinary 

 reagents cannot attack it, or so small in quantity that its colour 

 reactions are absent, even under the microscope. Bunge, however, in 

 the case of haematogen, had shown that ammonium sulphide has the 

 power of separating the iron ; and Mr. Bensley and myself ascer- 

 tained that this reagent has the same effect on isolated chromatin, 

 when kept in a warm condition for a long time in contact with the 

 substance, the iron separating as sulphide. I tried the effect of the 

 reagent on tissues, and took, for example, pieces of the mesentery of 

 Necturus, put them in a ground-stoppered bottle with ammonium 

 sulphide, and kept the bottle in a warm oven for several days. At 

 the end of that time, the pieces of tissue showed along the line of the 

 blood-vessels a greenish-blue colour, while the remaining portions had 

 a diffuse light-green colour. Under the microscope, the iron reaction 

 appeared in the red blood cells and their nuclei, while the remaining 

 cellular elements showed nothing further than a diffuse light-green 

 colour in both cell and nucleus. I found, moreover, that the same 

 results were obtained when the preparations were immersed in an 



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