VII.] ESTIMATION OF HEMOGLOBIN. 59 



5. Hsemin Crystals. Place some powdered dried blood on a 

 glass slide, or smear some blood on a slide, allow it to dry, add a 

 crystal of sodium chloride, and a few 



drops of glacial acetic acid. Cover 



with a cover-glass, and heat until 



bubbles of gas are given off. After 



cooling, brown or black rhombic 



crystals of hsemin are seen with a 



microscope (fig. 34). To preserve 



them irrigate with water, dry and ^ mhl Crystals . 



mount in Canada balsam. 



6. Detection of Blood-Stains. Use a piece of rag stained with 

 blood. 



(a.) Moisten a part of the stain with glycerine, and after a time 

 express the liquor, and observe it microscopically for blood-cor- 

 puscles. 



(b.) Tie a small piece of the stained cloth to a thread, place the 

 cloth in a test-tube with a few drops of distilled water, and leave 

 it until the colouring-matter is extracted. Withdraw the cloth by- 

 means of the thread. Observe the coloured fluid spectroscopi- 

 cally. 



(c.) Boil some of the extract with hydrochloric acid, and add 

 potassic ferrocyanide ; a blue colour indicates the presence of iron. 



(</.) Use the stain for the hsemin test, doing the test in a watch- 

 glass. 



7. The Hsemoglobinometer of Gowers is used for the clinical 

 estimation of haemoglobin (fig. 35). The tint of the dilution of a 

 given volume of blood with distilled water is taken as the index of 

 the amount of haemoglobin. The colour of a dilution of average 

 normal blood (one hundred times) is taken as the standard. The 

 quantity of haemoglobin is indicated by the amount of distilled 

 water needed to obtain the tint with the same volume of blood 

 under examination as was taken of the standard. On account of 

 the instability of a standard dilution of blood, tinted glycerin 

 jelly is employed instead. The apparatus consists of two glass 

 tubes of exactly the same size. One contains (D) a standard of 

 the tint of a dilution of 20 c.mm. of blood, in 2 cc. of water (i in 

 100). The second tube (C) is graduated, ioo = 2 cc. (100 times 

 20 c.mm.). 



(a.) Place a few drops of distilled water in the bottom of the 

 graduated tube (C). 



('>.) Puncture the skin at the root of the nail with the shielded 

 lancet (F), and with the pipette (B) suck up 20 c.mm. of the blood, 

 and eject it into the distilled water, and rapidly mix them. 



