220 THE AMERICAN MONTHLY [October, 



Crystals of liEemin ai^e prepared from dried blood. A small bit of 

 dried blood is placed on a slide, two or three drops of hydric acetate and 

 a few crystals of sodium chloride added and the slide heated over a flame 

 until bubbles of gas are given oft'. Allow the slide to cool, when the 

 crystal of haemin will form. The excess of the fluid is then carefully 

 absorbed with filter-paper, a drop of glycerine added and a cover-glass 

 put on and cemented with asphalt. 



Hsematoidin crystals are found in old blood extravasations. A bit of 

 an old apopletic clot, an extravasation in the subcutaneous tissue, or the 

 clot fi'om the corp7(s hitetim is teased up in a drop of glycerine, covered 

 and cemented. 



Permanent Preparations. — The two principal reagents that are 

 now used for the permanent preservation of blood cells are mercuric 

 chloride and osmic acid. The action of these reagents is not absolutely 

 perfect ; more or less of the red cells show slight changes. 



Mercuric chloride is used in the form of Pacini's* or Havem'sj solu- 

 tions. A drop of the solution is placed on the finger-tip and the latter 

 pricked through : the drop of fluid and the di^op of blood that flows out 

 is disseminated through the preservative wnth the point of the needle, 

 transferred to a slide, covered, and the cover immediately cemented. 

 Or I to 3 drops of blood are allowed to drop into a small glass cylinder 

 containing from lo to 15 c.c. of the preservative. The cvlinder is then 

 shaken so as to disseminate the cells through the fluid, and then allowed 

 to stand for 13 hours to allow the cells to settle. The cells are then re- 

 moved with a pipette and mounted in a drop of the preserving fluid. 

 The latter method is best for the blood of animals. 



Osmic acid is used in the strength of i"o. The method of procedure 

 is the same as the second method described above. After the cells have 

 been fixed with the osmic acid [after remaining in the acid for 12 hoursj 

 the osmic acid solution is poured oft" and the cells washed several times 

 with distilled water, and then hardened in So% alcohol. They can be 

 preserved in this for any length of time, a few being taken up with a 

 pipette and mounted in glycerine. 



Gage^ s Method for Amphibian Blood. — Three to four drops of fresh 

 blood are allowed to fall into 10 c.c. of normal salt solution, contained 

 in a tall glass cylinder. Agitate thoroughly, and mix with roo c.c of 

 a saturated aqueovis solution of picric acid with constant stirring. Al- 

 low' the blood cells to settle, and pour oft' as much of the supernatent 

 fluid as possible, add an equal amount of normal salt solution, continue 

 this until the salt solution is onlv slightly tinged yellow. Then add 10 

 c.c. of a mixture of ^ parts of carmine and 95 parts of picro-carmine for 

 staining. This will require about 15 hours. Then pour ofl' as much 

 of the staining fluid as possible, and add 10 c.c. of acid glycerine [gly- 

 cerine 100 c.c. hydric acetate or formic acid 1 c.c] The cells may 

 be kept in this mixture indefinitely. For mounting, remove a drop 

 with a pipette, place it on a slide cover, and cement the cover imme- 

 diately. 



* Pacini's Fluids. A. Mercuric chloride, i gm., sodium chloride, 4 gms., distilled water, 200 c.c. 

 B. Mercuric chloride, 1 gm., sodium chloride, 2 gms., distilled water, 200 c.c. The solution A is lor 

 the blood of warm-blooded animals, B for the cold-blooded. 



t Hayem's Fluids. A. Distilled water, 200 c.c, sodium chloride, i gm., sodium sulphate, $ gms., 

 mercuric chloride, 0.5 gms. B. Distilled water. 200 c c. sodium chloride, i gm., sodium sulphate, 5 

 gms., mercuric chloride, 0.5 gms., glycerine [28 B.], 10 gms. 



