344 THe MIcROSCOPE. 
DETECTION OF BLOOD STAINS.—Some puzzling murder cases have 
drawn much attention to the difficulties attending an accurate 
diagnosis of the nature and origin of blood stains. When of 
quite recent date, the microscope may reveal their origin, by the 
form, diameter, and characters of the red corpuscles. But when 
the stains are older, and the blood is in a state of more or less 
decomposition, these means will be insufficient, for the hemo- 
globin will have changed into hydrochlorate of hematin. These 
are minute, rhomboid, brownish crystals, varying in size in 
different animals, and requiring a power of about four hundred 
diameters to render them visible. If these crystals can be de- 
monstrated, the stain is surely blood; in their absence, spectrum 
analysis will be required. To obtain the crystals, a fragment of 
the dried blood is placed on a slide, dissolved in a drop of water. 
A minute piece of sea-salt is added ; it is covered with another 
thin slide, and pure acetic acid is passed between the two. It is 
then heated to boiling point, and acetic acid re-applied, repeat- 
ing the process until the crystals are deposited. Or, a smaller 
quantity cf the blood may be rubbed with chloride of sodium, 
then boiled with glacial acetic acid; this mixture, when evapor- 
ated to dryness, will yield the crystals. Blood corpuscles are 
destroyed in many ways, by hot water, acetic, gallic, hydro- 
chloric, sulphuric acids, solutions of potash or soda, chloroform, 
ether, and other agents. The best preservative of blood is an 
imitation serum, made with amniotic fluid, to which a few drops 
of tincture of iodine have been added. This will save both red 
and white corpuscles and the particles of fibroid, if the stains be 
wetted with it before decomposition. Alcohol, chromic and 
picric acids, and bichromate of potash will also preserve blood 
stains.—Medical World. 
DEXTRIN AS AN EMBEDDING MATERIAL FOR THE FREEZING MIC- 
RoOTOME.—Mr T. L. Webb writes to the Provincial Medical Journal 
for August as follows: I find that by taking an aqueous solution 
of carbolic acid (about 1 in 40), and dissolving therein sufficient 
dextrin to make a thick syrup, a medium is obtained which is 
superior to the time-honored gum and sugar, in three ways: It 
freezes so hard as to give a firm support without being too hard; 
it keeps better than gum, in which several kinds of fungi are apt 
