2O2 PPIYSIOLOGICAL CHEMISTRY. 



IV. Fibrin. 



1. Preparation of Fibrin. Allow blood to flow directly from 

 the animal into a vessel and rapidly zvhip it by means of a bundle of 

 twigs, a mass of strong cords or a specially constructed beater. 

 If a pure fibrin is desired it is not best to attempt to manipulate 

 a large volume of blood at one time. After the fibrin has been 

 collected it should be freed from any adhering blood clots and 

 washed in water to remove further traces of blood. The pure 

 product should be very light in color. It may be preserved under 

 glycerol, dilute alcohol or chloroform water. 



2. Solubility. Try the solubility of small shreds of freshly 

 prepared fibrin in the usual solvents. 



3. Millon's Reaction. Make the test according to directions 

 given on page 90. 



4. Hopkins-Cole Reaction. Make the test according to direc- 

 tions given on page 101. 



5. Biuret Test. Make the test according to directions given 

 on page 92. 



V. Detection of Blood in Stains on Cloth, etc. 



1. Identification of Corpuscles. If the stain under examina- 

 tion is on cloth a portion should be extracted with a few drops 

 of glycerol or normal (0.9 per cent) sodium chloride solution. A 

 drop of this solution should then be examined under the micro- 

 scope to determine if corpuscles are present. 



2. Tests on Aqueous Extract. A second portion of the stain 

 should be extracted with a small amount of water and the follow- 

 ing tests made upon the aqueous extract : 



(a) Hcemochromogen. Make a small amount of the extract al- 

 kaline by potassium hydroxide or sodium hydroxide, and heat 

 until a brownish-green color results. Cool and add a few drops of 

 ammonium sulphide or Stokes' reagent (see page 203) and make a 

 spectroscopic examination. Compare the spectrum with that of 

 hsemochromogen (see Absorption Spectra, Plate II). 



(b) H&min Test. Make this test upon a small drop of the aque- 

 ous extract according to the directions given on page 197. 



(c) Guaiac Test. Make this test on the aqueous extract accord- 

 ing to the directions given on page 196. The guaiac solution may 

 also be applied directly to the stain without previous extraction in 

 the following manner : Moisten the stain with water, and after 

 allowing it to stand several minutes, add an alcoholic solution of 

 guaiac (strength about I : 60) and a little hydrogen peroxide or 



