THE BLOOD. 2 19 



ture, coagulation follows. The effect of the sodium sulphate is to prevent 

 coagulation. In this case dilution favors it. 



Ex. Pour some fresh blood into a clean vessel and stir it thoroughly 

 with a glass rod, if a small quantity in a beaker is taken, or with a stick 

 if a larger volume, as of slaughter-house blood, is used. The fibrin gradu- 

 ally separates, and entangles most of the corpuscles. Save the serum for 

 tests to be explained and wash the crude fibrin thoroughly under running 

 water to remove the corpuscles and coloring matter. The well-washed 

 fibrin is white and stringy. Fibrin so prepared is employed in many ex- 

 periments, especially in illustrating digestion phenomena. On the large 

 scale it is used in the manufacture of peptone. 



Ex. To illustrate the ready digestion of fresh fibrin use about half a 

 gram with 10 cc. of 0.25 per cent hydrochloric acid. Keep the mixture 

 some hours at 40 C. The fibrin gradually dissolves to form acid albumin, 

 which may be obtained in solution by filtering from any undigested residue. 

 The careful addition of a little sodium carbonate solution produces a pre- 

 cipitation of the acid albumin. 



BLOOD TESTS. 



The serum left after separation of the fibrin by stirring, con- 

 tains much of the blood coloring matter and may be used as 

 well as the fresh blood for many tests, some of which will be 

 illustrated here. 



Ex. GUAIACUM TEST. To a little blood solution in a test-tube add some 

 fresh tincture of guaiacum and then a few drops of an ethereal solution 

 of hydrogen peroxide. Shake the mixture and observe that the precipi- 

 tated resin has assumed a blue color, more or less marked. In this test 

 turpentine oil, which has been shaken with air in a bottle, or which has 

 been exposed to the air, can be used instead of the solution of peroxide. 

 Hydrogen peroxide is developed by the action of oxygen on turpentine. 

 In this test the hemoglobin seems to act as a carrier of oxygen to the 

 resin. The oxidation product of the resin is blue. 



Ex. HYDROGEN PEROXIDE TEST. A reaction somewhat similar to the 

 above in principle is observed on mixing 2 cc. of the blood with 10 cc. 

 of the commercial hydrogen peroxide solution. The hemoglobin brings 

 about the decomposition of the peroxide with liberation of oxygen, which 

 escapes, producing froth. 



Reaction of Blood. The normal reaction of blood is alka- 

 line, which cannot be observed, however, in the usual way 

 because of the marked color of the pigment. It may be readily 

 seen by working in the following manner : 



Ex. Prepare some small smooth plaster of Paris surfaces by pouring 

 the well-known plastic mixture of plaster of Paris and water on glass 



