PROTEINS 247 



into two, a broad dark band in the green between b and F, and a 

 narrow fainter band to the left of E. A fourth band may appear 

 on the violet side of D. 



(h) Hemochromogen. (Reduced alkaline Hematin). To 

 blood diluted 1-5 add half its volume of 10% sodium hydrate, and 

 warm almost to boiling. The liquid now contains alkaline 

 hematin, which shows a single absorption band, usually rather 

 faint, lying across D, and mainly toward the red end of the spec- 

 trum. To this alkaline hematin solution, add Stokes' reagent. 

 The liquid now contains hemochromogen. Chart the spectrum. 

 The formation of hemochromogen is a very delicate test for blood 

 stains, as solutions of hemoglobin too dilute to give a character- 

 istic spectrum, will give, upon conversion into hemochromogen by 

 boiling with 1% sodium hydrate and reduction with Stokes' rea- 

 gent, a single band in the green near the yellow. 



(i) Acid Hematoporphyrin. To 5 c.c. of concentrated sul- 

 phuric acid in a test tube add 2-3 drops of undiluted defibrinated 

 blood, mixing well after the addition of each drop. Observe the 

 color and chart the spectrum. If the color is too dark, dilute 

 with glacial acetic acid. 



ii. Crystallization of Blood Pigment. 



(a) Hemoglobin Crystals. Place a drop of defibrinated rat 

 or guinea pig blood on a slide, add an equal volume of water and 

 1-2 drops ether. Mix and cover. In a few minutes crystals of 

 oxyhemoglobin separate out. Observe under the microscope and 

 draw. 



iii. Cliemical Tests for Recognizing the Presence of Blood. 



(a) Hemin Crystals. Place a drop or two of blood on a slide. 

 Add one or two crystals of sodium chloride (no more) and rub 

 with a glass rod until the salt has dissolved. Place the slide on 

 a ring about a foot above a small flame and allow the blood to 

 evaporate slowly to complete dryness. Rub the red residue to a 

 powder with a knife blade, collect the powder in a small pile and 

 add a drop of glacial acetic acid from a glass rod. Rub to a 

 paste, place a portion on a clean slide, and add a drop of glacial 

 acetic acid. Cover with a cover slip and cautiously heat over a 



