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 haemoglobin 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 

 7.5/1 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 



