'New Way of 'producing Colour-Contrast. By J. Bheinberg. 385 
completely explain, a greater penetrating power, especially with the 
low-power method, and sections which are too thick for viewing in 
the ordinary way appear quite distinct when this method is applied ; 
semiopaque preparations such as bone, where it is often difficult to 
get very thin sections, show up especially well. 
I am in hope, therefore, that the method may prove of service to 
the general medical practitioner and student, where a rapid examina- 
tion of sections or objects may be desirable, and where careful cutting 
and staining are impossible or might take too long. Of course, as far 
as staining is concerned, it only applies to such objects where the 
raison d'etre of the staining is for the sake of general contrast 
with the background, as it is obvious that it cannot in any way replace 
selective staining. Stained preparations themselves also show up 
well on a background of other colour, notably again such as are too 
thick to be seen well by ordinary methods. 
Secondly, it is available in that important class of research — the 
observation of living organisms. At present we have few means of 
sufficiently clearly differentiating the structure of living organisms, 
except by the aid of one or two stains such as Bismarck-brown, or by 
dark-ground illumination. The colour-disc method seems particularly 
to make the internal organs stand out more distinctly. With such 
living organisms as naturally show different colours in different parts, 
better results can be generally obtained with discs the centre only of 
which is coloured, because a coloured rim suppresses the natural 
diversity of hue to a great extent. 
For crystals and other mineralogical specimens the method is very 
suitable, since it shows up their form more than otherwise. 
For the examination of commercial fibres, as silk, wool, cotton, 
and for viewing thin fabrics, it is useful, as it admits of the fibres or 
threads being counted more readily, apart from increased distinctness 
of structure. I may mention that with one of the discs as described 
before, for throwing red and blue light on the object in directions at 
right angles to each other, I have been able to make the weft of a 
finely woven cloth appear completely red, whilst the warp appeared 
blue. 
The next class of objects for which I believe it to be of value are 
those where we deal with resolution of striae or dots, e.g. diatoms, 
and all objects which refract and diffract light strongly in a regular 
manner. The whole system of the colour-disc illumination being 
based upon refraction and diffraction, such objects are naturally suit- 
able to experiment with, and generally, lend themselves easily to a 
variety of results apart from those obtained by use of the ordinary 
concentrically arranged colour-discs. If the striations consist of 
ridges, we can, with the low-power method, cause the opposite sides 
of the ridges to assume different colours. If there are sets of striations 
in different directions, we can likewise differentiate them in colour. 
By means of the modified colour-discs to which I have already 
