PHYSIOLOGICAL CHEMISTRY 333 



add a few drops of calcium chloride solution. To d add an equal 

 volume of saturated sodium chloride solution. Filter off the flocculent 

 precipitate and keep for the next experiment, which should be per- 

 formed as soon as possible. To the filtrate add some calcium chloride 

 solution. Place all in a water bath at 37 C. It will be found that a 

 has not clotted, that b and c have clotted, that the filtrate d has not 

 clotted. 



From these experiments, we gather (1) that blood will not clot when 

 the calcium salts have been removed by an oxalate ; (2) that serum can 

 clot oxalate blood (that is, blood without the presence of calcium salts), 

 because it contains the necessary enzyme already formed in it; (3) that 

 oxalate blood will clot when calcium is added to it, because with free 

 calcium available the coagulating enzyme is formed ; (4) that the body 



FIG. 227. Collection of blood. 



coagulated is a protein thrown out of solution by half saturation with 

 sodium chloride solution. This body is known as fibrinogen. It is 

 insoluble in distilled water and easily thrown out of solution by 

 saturation with salts, and, therefore, belongs to the globulin class of 

 proteins. 



EXPERIMENT IV. Quickly redissolve in water the precipitate 

 obtained in Experiment III. d. The salt adhering to the precipitate forms 

 a dilute saline solution, in which the precipitate dissolves. Test the 

 solution obtained for protein by the colour tests. 



EXPERIMENT V. Into the bent capillary tubes provided collect, as 

 shown in Fig. 227, some of your own blood, first introducing a small 

 quantity of anti coagulant fluid, preferably 10 % sodium citrate, since 

 sedimentation is most rapid with this solution ; 1 % potassium oxalate 

 or 3 % sodium fluoride may also be used. Having sealed off" the ends, 

 under the demonstrator's supervision, hang it upon the centrifuge by 

 the bent end. With the plasma so obtained, perform experiments such 



