MICROSCOPICAL DIAGNOSIS. 31 



fourths of an one per cent, solution) is placed to the edge of the 

 cover and allowed to run under and moisten the specimen. The 

 specimen is examined now with the highest power at command. If 

 the particles of clot are so deeply colored that the corpuscles are in- 

 distinct, then the color may be washed out by placing some of the salt 

 solution at one edge of the cover and a piece of blotting paper at 

 the opposite edge. Care should be used not to move the cover- 

 glass during the operation. If found desirable, all the color can be 

 removed from the clot in this way. Try again to see the corpuscles 

 sufficiently well to be able to measure them. If they are too pale 

 they may be colored. Sometimes a drop of iodized- serum will 

 suffice, added cautiously to the edge of the cover. Weak solutions 

 of bdine have proved the best of anything for this purpose in our 

 hands. We do not believe this coloring changes the diameter of the 

 corpuscles in the least. Those corpuscles most perfect in shape 

 should be chosen for measurement. 



Persons have testified, as experts, in criminal cases, and have 

 accurately described their methods and measurements of corpuscles, 

 and have actually sworn that the stain they examined was composed 

 of human blood, when upon closer examination in the hands of 

 genuine experts the corpuscles were proved to be vegetable spores. 

 There is scarcely a microscopist in this country that does not 

 remember the details of the case to which we refer. Let it be 

 remembered that potassic hydrate and glacial acetic acid will com- 

 pletely destroy the blood corpuscles in a short time, but will not 

 materially affect the spores of the vegetable kingdom. 



We are not able to give any positive distinctions between the 

 blood-crystals of the various animals sufficient to make them of 

 value in criminal cases. 



The blood of most of the mammalia, including man, generally 

 yields prismatic or rhomboidal crystals. The blood of the guinea- 

 pig crystallizes very easily, giving beautiful tetrahedral crystals. In 

 the squirrel the crystals are hexagonal tables. To obtain hsemin 

 crystals, a drop of blood is placed in a watch crystal and about 

 twenty times its bulk of glacial acetic acid added. The mixture is 

 then warmed, and as it evaporates the desired crystals will be 

 formed; or, to a drop of dried human blood add a few crystals of 

 common salt, cover with a thin glass and place a drop of glacial 

 acetic acid to its edge, allowing it to run under and come in contact 



