28 THE AMERICAN MONTHLY [Feb 
It is surprising to consider what a large variety of 
most interesting slides exhibiting a great variety of 
stained tissues can be made from the eye. This field has 
not been worked by amateurs and such slides are rare as 
they would be useful. Cholestearin crystals appear as 
thin transparent rhombic plates often notched at the an- 
gles. A little sulphuric acid colors them orange, or later 
a beautiful rose-red, Lugol’s solution of iodine (1), iodide 
of potassium (2), and water (100), colors the crystals dark 
brown which can be changed to bright blue by a mere 
trace of sulphuric acid. (Too much acid dissolves the 
crystals.) The various kinds of degeneration yield ma- 
terial for stained objects in abundance. Fibrin is shown 
in an intense blue color by means of Weigert’s specific 
stain made of gentian-violet. By fine particles of iron 
getting into the eye and becoming dissolved therein, tis- 
sues become laden with this metal. This can be demon- 
strated by coloring a fine blue color by means of Perls’ 
reaction with Berlin blue and alum-carmine. The beau- 
tiful iron particles are perfectly demonstrated. By the 
same reaction, copper, if present, is shown to be colored 
brown through the precipitation of ferrocyanide of cop- 
per. Likewise, mercury can be condensed and precipi- 
tated in bluish-black crystals making an elegant slide. 
Indeed, the beauty of a collection of slides, produced by © 
the clearly-described processes of Greeff, is not inferior 
to any in biology unless we except the always-to-be-ex- — 
cepted diatoms. 
A second and greatly improved era in staining has of 
late been inaugurated by a trio of Europeans consisting 
of Comillo Golgi of Pavia, P. Ehrlich of Berlin, and Ra- 
mon y Cajal of Madrid. Instead of painting cells they 
impregnate cells with coloring matter and thus differ- 
entiate from each other different kinds of cells. Only in 
this way can details be secured. This new era has come 
within the past 20 years and its importance is not yet 
