284 Dr. A. B. Macallum. On the Demonstration 



In the smaller cells, the reaction seems to differentiate between the 

 chromatin and linin parts of the filament. 



I may state also, that by this method the iron-holding compound 

 of the muscle-fibre in Oniscus is found to be confined to its dim 

 bands. 



I have repeatedly employed the hydrochloric acid and potassic 

 ferricyanide mixture to show that the green or greenish -black com- 

 pound resulting in the nuclei from the action of ammonium sulphide 

 is ferrous sulphide. For this purpose, the nuclei, which are rich in 

 chromatin, e.g., those of the testicular cells and of the immature 

 ovarian ova in Necturus, are the best. Usually I washed out the 

 glycerine and sulphide mixture from under the cover-glass by the 

 addition of a large drop of a mixture of equal parts of glycerine and 

 water, and, after some hours, when it had run under the cover, a 

 strip of paper touching the opposite side drained away a portion of 

 this. A repetition of this process several times left very little 

 sulphide, and, very often, few cells under the cover. The addition 

 now of a drop of a mixture of weak hydrochloric acid, and of freshly 

 prepared potassic ferricyanide led to the formation in the previously 

 green or greenish -black nuclei of a deep aznre-blue colour, strictly 

 limited to the parts originally affected with the ammonium sulphide. 

 This reaction is sharp, and comes out almost immediately, whereas 

 when hydrochloric acid and potassic ferrocyanide are used, the blue 

 reaction comes out in about half-an-hour, and the colour seems to 

 diffuse through the nucleus and sometimes into the cell. The acid 

 and ferricyanide mixture I have also employed successfully on the 

 nuclei of the cutaneous epithelium, and of the hepatic, gastric, intes- 

 tinal, and pancreatic cells of Necturus, which had previously reacted 

 with ammonium sulphide. In no case was it found that the imme- 

 diate application of the acid reagent mentioned, or of acid ferro- 

 cyanide solution, gave the slightest reaction with those species of 

 nuclei which required a more or less lengthy contact with ammonium 

 sulphide in order to develop the iron reaction. In every particular 

 instance referred to, the latter reagent had to be employed to decom- 

 pose the chromatin, and set free its iron as sulphide, and the acid 

 mixtures then, and then only, gave a deep azure-blue colour. 



Now it might be urged that this iron reaction is due to haematin 

 or an allied iron compound. The observations which I now proceed 

 to detail will, I think, completely meet this objection. 



Believing that if iron enters into the composition of the chromatin 

 of the animal cell, it must be also present in that of the vegetable 

 cell, I asked Mr. Bensley to employ my method in studying the dis- 

 tribution of iron in the latter. His investigations, so far as they 

 have gone, have confirmed mine, since he has found that the chro- 

 matin of the pollen cells of Dianthus, Cucurbita, Narcissus, and of the 



