PRACTICAL EXERCISES 



59 



increased by pressure on the abdominal walls, which squeezes it 

 towards the heart, by passive pumping movements of the hind-legs, 

 and also during the convulsions of asphyxia, which soon appear. 

 Notice that the blood begins to clot in a few minutes, and that 

 very soon the vessel can be tilted without spilling the blood. Set it 

 aside in a cool place, and observe next day that some clear yellow 

 serum has separated from the clot. 



(7) Observe that the blood in o and ft has not coagulated. Label 

 four test-tubes A, B, C, D, 



and put into each about 5 c.c. 

 of the oxalated blood. Add 

 to A and B 5 or 6 drops of a 

 2 per cent, solution of calcium 

 chloride, to C 12 drops, and 

 to D as much as there is of 

 the blood. Leave A at the 

 ordinary temperature, put the 

 other test-tubes in a water- 

 bath at 40 C-, and note when 

 clotting occurs. 



(8) By means of a centri- 

 fuge (Fig. 12) separate the 

 plasma from the corpuscles in 

 a and 8. (With Jung's hand 

 centrifuge fairly clear oxalated 

 plasma may generally be ob- 

 tained in about twenty 

 minutes. Magnesium sulphate 

 [' salted '] plasma usually takes 

 a little longer to separate.) 



With the decalcified plasma 

 from ft repeat the observations 

 in (7). 



With the plasma from a 

 perform the following experi- 

 ments : (a) Put a small quan- 

 tity of the plasma into eight 

 test-tubes, labelling them E, 

 F, G, H, I, K, L, and M. 

 Dilute E and F with ten times, 

 and G and H with five times, 



FIG. 12. CENTRIFUGE QUNG). 



The four cylinders shown at the top of 

 the figure are so swung that they become 

 horizontal as soon as speed is got up. 



as much distilled water as was taken of plasma ; dilute the plasma 

 in I and K with ten times, and in L and M with five times, its 

 volume of a solution of fibrin-ferment containing some calcium 

 chloride. Put E, G, I, and L in the bath at 40 C., and leave the 

 rest of the test-tubes at room temperature. Observe in which of the 

 test-tubes, if any, coagulation occurs, and the time of its occurrence, 

 and report the result. 



If no centrifuge is available, the decalcified and salted blood must 

 be left standing in a cool place for twenty-four hours or more till the 



