LESSON XXI 



COAGULATION OF BLOOD 



1. Effect of decalcifying Agents in hindering Coagulation. From an 

 anaesthetised dog collect samples of blood from the carotid artery, into 

 which a suitable cannula should have been previously inserted. 



(a) Collect the first sample in an equal volume of 0-4 per cent, solution 

 of potassium oxalate made with physiological salt solution. 



(6) Collect the second sample in an equal volume of 0'4 solution of 

 sodium fluoride. 



(c) Collect the third sample in a quarter of its volume of 10 per cent, 

 solution of sodium citrate. 



In all three cases mix thoroughly, and coagulation is hindered owing to 

 decalcification, as explained on page 106. 



The separation of the plasma from the corpuscles may be most readily 

 carried out by a centrifugal machine, one form of which is shown in the 

 next figure; the corpuscles settle and the supernatant plasma can be 

 then pipetted off. Sedimentation is specially rapid in the case of citrate 

 blood, and a well-marked layer of colourless corpuscles and platelets may 

 usually be seen on the top of the mass of red corpuscles. 



Oxalate plasma and citrate plasma coagulate on the restoration of the 

 calcium by adding a few drops of calcium chloride solution, as we have 

 already seen in the elementary course (p. 101). Fluoride plasma does not 

 coagulate unless fibrin ferment (or some fluid such as serum which contains 

 fibrin ferment or thrombin) is added as well as the calcium salt. Fluoride 

 plasma thus forms a convenient test-fluid for fibrin ferment. 



If in either case the plasma is previously heated to 60 C. and filtered, 

 coagulation that is to say, fibrin formation can never be produced, because 

 its mother-substance, fibrinogen, which is coagulated by heat at 56 C., has 

 been destroyed and removed. 



2. Influence of Leech Extract on Coagulation. The same dog still under the 

 anaesthetic may be next used for the following experiments : 



(a) Draw off a sample of blood into a clean test-tube, and note the time 

 it takes to clot. 



(6) Draw off a second sample into about half its volume of leech extract, 

 made by grinding up the heads of about twenty leeches in '20 c.c. of salt 

 solution, and filtering. This remains unclotted for hours or days. 



(c) Inject 10 c.c. of the extract into the jugular vein of the animal, and 

 draw off samples of blood from time to time, comparing the coagulation 

 time (which gradually lengthens) with that of specimen a. 



(d) Having obtained a specimen which does not clot at all, dilute it with 



