60 



233. To another portion of the plasma add a little fibrin- 

 ferment prepared by the demonstrator. The fibrin-ferment is 

 prepared as follows : Take fresh fibrin, wasli it under a tap 

 with water (best in a piece of cotton) until perfectly colorless. 

 Squeeze out the water and cover the fibrin with an 8% solution 

 of sodium chloride. After a few hours, if the solution is fil- 

 tered it will show the presence of the ferment. 



Another method is : Precipitate some blood serum with about tin times its 

 volume of alcohol. Let it stand for several weeks, then extract the precipitate 

 with water. The water dissolves out the fibrin-ferment, but not the other coag- 

 ulated proteids. 



234. Add a drop of freshly prepared tincture of guaiacum 

 to a small amount of diluted defibrinated blood, and then 

 some hydrogen peroxide or old oil of turpentine. The color 

 changes to blue. This is often used as a test for hemoglobin, 

 but other substances (oxygen carriers) give a blue color under 

 the same conditions. 



235. Place some hydrogen peroxide over fresh fibrin in a 

 watch glass ; bubbles of oxygen are given off. 



236. Immerse a flake of fibrin in freshly prepared tincture 

 of guaiacum, (5% of pure resin in alcohol) and then immerse 

 the flake in hydrogen peroxide. A blue color is developed, 

 due to the ozone liberated by the fibrin and forming a blue 

 color with the resin. Compare 234. 



237. The proportion of the corpuscles to the plasma of 

 the blood may be quite readily obtained by the use of the 

 hematocrit in connection with the centrifuge. The Hemato- 

 crit consists of a graduated glass tube 50 mm. in length and 

 0.5 mm. bore, to receive the blood. The tube is marked by 

 a scale ranging from to 100, the scale being rendered visible 

 by a lens front (prism form). The outer end of the tube fits 

 into a small cup-like depression at the end of the arm, the 

 bottoms of which are covered with the rubber disks, while the 

 inner extremity is held in position by a spring. 



To use the Hematocrit in blood examinations proceed as 

 follows : — The rubber tube with mouthpiece at one end is 

 slipped over the end of the Hematocrit, and the latter is filled 

 by suction on the mouthpiece, from a drop of blood obtained 

 by a prick of the finger. The blunt end of the tube is next 

 quickly covered with the finger tip, and the tube is inserted 



