70 EXPERIMENTAL PHYSIOLOGY 



shake from time to time. Does this affect the rate of 

 clotting? 



Place Bottle 7 with 1, 2, and 5. Examine after three days. 

 Has this blood clotted? What is missing in it? (The sub- 

 stance is called fibrin.) 



Summarize -the conditions best suited to clotting. The 

 exact reason why blood clots when it is not in a healthy 

 blood vessel is unknown. 



B. Study of the Clot. Pour off the liquid from all the 

 bottles in which a clot has formed and place it in Bottle 8. 

 (This liquid is called serum.) Then break one of the bottles 

 containing a clot and remove the clot entire. What is its 

 shape? color? consistency? Cut off a thin slice of it and 

 examine it under the microscope. What parts can you 

 distinguish? Does it contain any corpuscles? The jelly- 

 like substance is to be found in its pure state in Bottle 6. 

 Examine some of this fibrin. What is its color? Test it 

 for proteid. What is the result? Explain in a few words 

 the formation of a clot and the* part played in its formation 

 by the fibrin and the corpuscles. 



C. Study of tJie Serum. Examine the liquid in Bottle 8. 

 What is its color? Why is it not red? 



Test a little with iodine solution for starch. Since starch 

 must be digested before it can be absorbed into blood, why 

 should you expect this result? 



Test some of the serum with Fehling's solution for the 

 presence of grape sugar. Do you get a strong test? What 

 does this result suggest as to the amount present? 



Burn a little serum on a piece of platinum foil. Does it 

 contain any mineral matter? 



Place a drop on a piece of unglazed paper and let it 

 evaporate. Does it leave a grease spot? 



