SUGGESTIONS FOR LABORATORY WORK 609 



COAGULATION OF BLOOD 



Draw a drop of blood, as described above, but do not remove 

 it from the finger. Rest the hand in a comfortable position. Test 

 the consistency of the blood-drop by drawing a hair through it 

 Repeat the test at intervals of one minute till no further change 

 occurs. Observe the changes that take place in the drop of blood 

 during the process of coagulation. 



Coagulation Time. When blood clots it sets first into a soft jelly 

 which is firm enough, however, to support a small weight. Ad- 

 vantage is taken of this fact in the Dak Coagulometer. A fine 

 glass tube, about J/2 inch long, is to be filled, by suction, with 

 freshly drawn blood. A small shot placed in the tube will run 

 along it when the tube is inclined so long as the blood is uncoagu- 

 lated, but will remain stationary as soon as clotting occurs. 



Congest the finger as above, and after two sharp prickings with 

 a needle, near together, squeeze out a good sized drop of blood. 

 Suck the fine tube nearly full. Insert the small shot as quickly as 

 possible. The ends of the tube need not be plugged, since surface 

 tension will retain the shot in the blood. Note the minute and 

 second at which the blood was drawn. Thirty seconds thereafter 

 hold the tube upright with the shot at the top. If the shot runs 

 down repeat at thirty second intervals until it fails to move. The 

 elapsed time is coagulation time. To check the result the experi- 

 ment may be repeated. 



The Importance of Calcium in the Coagulation Process. Prepare to 

 repeat the above described experiment on coagulation time. After 

 the blood is drawn and before sucking it into the tube sprinkle into it 

 three or four grains of powdered sodium oxalate. This substance 

 removes the calcium from the blood by precipitation. Continue 

 the experiment for twice the coagulation time previously deter- 

 mined. If the blood has not then clotted discontinue the experi- 

 ment. Interpret the result. 



Coagulation Time in a Lower Animal. The experiment on coag- 

 ulation time may be varied by using, instead of human blood, blood 

 drawn directly from the vessels of a turtle, with brain destroyed 

 and plastron removed, into the tube of the coagulometer. Deter- 

 mine carefully the coagulation time for the turtle. Compare with 

 the coagulation time of human blood. 



