128 ELEMENTS OF APPLIED MICROSCOPY. 
sixty years after his death on the papers which lay upon 
his desk. 
For examination by the microspectroscope, fresh. 
blood-stains are treated with distilled water and older 
specimens with weak acetic or citric acid. When placed 
in a small glass cell and examined by the methods to be 
described in the next section, the characteristic spectrum 
of hemoglobin or one of its derivatives will be apparent. 
The direct microscopical examination of blood-stains 
aims simply at the detection of the red corpuscles 
and serves to distinguish mammalian blood from that 
of birds, the three tests above outlined being general 
for the hemoglobin of all red-blooded animals. Dried 
and clotted blood must first be treated with some 
solvent which shall attack the albuminous coagulum 
and set free the blood-cells. Numerous media have 
been suggested, of which a 33% solution of potassium 
hydrate is one of the simplest, and Ranvier’s solution 
(potassium iodide, 2 parts; saturated aqueous solution 
of iodin, 100 parts) is one of the best. In any case a 
bit of clot or the scraping from a stain is covered with 
the solvent and placed in a hollow slide under the micro- 
scope. Sometimes after a few minutes, sometimes only 
after days, the opaque mass becomes clearer and the 
individual cells appear as circular, non-nucleated discs 
4.5 # in diameter. Under most conditions the discs 
appear somewhat biconcave, with a thickened ring about 
the edge. 
In the original process of drying or in the treatment 
with a solvent, the blood-cells may be so distorted that 
