86 HuGGiNs, on the Spectra of Microscopic Objects. 
microscope are not self-luminous, as are the stars and ter- 
restrial flames. The microscopist can hope to profit by the 
use of the prism in the case alone of those substances which 
modify by a special absorption the light by which they are 
rendered visible, either during transmission or reflection. The 
discoveries, however, of Professor Stokes in connection with 
the peculiar optical characters of blood and chlorophyll show 
that even this restricted field of investigation is one of con- 
siderable promise. 
By means of the apparatus described below, the spectrum 
of any part of a microscopic object can be examined apart, 
and also can be compared with the spectra of the adjoining 
portions of the object. 
In this manner the spectrum of a single blood-disc, or the 
spectrum of the contents of a single cell, can be observed, and 
any changes in living tissues which cause a modification of 
the spectrum can be watched and investigated. 
Possibly microscopical physiology may receive some aid 
from this way of using the prism, since the deepest object- 
glasses, even the and may be employed. 
This method of prismatic observation is equally suited to 
an examination of the light reflected from diflPerent parts of 
an opaque object. 
Essentially the plan consists in arranging the slit of an 
ordinary spectrum apparatus in the place of the eye-piece of 
the microscope. 
The spectrum apparatus may be of any form, may be sup- 
ported on a separate stand, or be made to form part of the 
microscope. 
