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IRON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS. 265 
stance, and when subjected to the action of artificial gastric 
juice for two or three days it lessens slightly in volume, but 
its presence is quite as readily demonstrable then as it was 
previously. In this case the central portion of the cell also 
diminishes in volume slightly, the diminution entailing a 
shrinkage of the peripheral portion away from the original 
limits of the cell. Digestion does not affect the capacity, 
on the part of the central substance or of the membrane of 
the vesicles referred to, of absorbing staining matters, but on 
subsequently treating such preparations with a solution of 
potassium hydrate of 0-1 per cent. strength for twenty-four 
hours, the vesicles disappear and the central body, now some- 
what swollen, has lost its capacity for fixing colouring matters 
in itself. Evidently there is here a substance which has the 
characters of nuclein. This is confirmed by the results of 
experiments to determine the presence of ‘ masked” iron. 
The central body always gives, with the glycerine and sul- 
phide mixture, in an interval of from two or three days to 
two weeks in length, depending apparently on the size of the 
cell, a diffuse greenish reaction which is changed to light blue 
on the addition of a drop of an acid ferrocyanide solution. 
When granules and vesicles stainable with hematoxylin are 
present, they also give a reaction for iron, but it does not 
always manifest the same intensity. The iron in them is most 
readily demonstrated after they have been treated with sul- 
phuric acid alcohol (fig. 51). 
2. In the peripheral portions of the cytoplasm, in well- 
nourished forms only, are granules not so readily stainable 
with hematoxylin, but which are intensely coloured with picro- 
carmine. These are dissolved out of the fresh cell with dilute 
hydrochloric ac id, and even in preparations thoroughly hard- 
ened in alcohol they are but slightly less soluble in the same 
reagent. In Oscillariz they are placed in a row at each end 
of the cell and adjacent to the transverse walls, but in Micro- 
coleus terrestris and Cylindrospermum majus they are 
disposed in all the peripheral portions of the cytoplasm. In 
the spores of the latter some of them appear as if embedded 
