III.] COAGULATION OF BLOOD. 49 



water, and determine that the mixture coagu- 

 lates very slowly. 



Take another 2 c.c. of plasma, and add to it 16 c.c. 

 of an aqueous solution of prepared fibrin fer- 

 ment'; coagulation will quickly take place. 



16. Dilute serum ten-fold with water and with it 

 observe the following general reactions of pro- 

 teids. (If sufficient serum is not obtainable, 

 take the white of an egg, cut through the 

 membranes in several places with scissors, add 

 60 vols, of water, beat up well, filter through 

 flannel and then through filtering paper.) 

 a. Xanthoproteic reaction. Take a little of the 



^ The student may prepare fibrin ferment in one of tlie following 

 ways: 



a. Let blood run into 10 times its volume of water, tilt it upside 

 down once or twice so tbat tbe fluids are well mixed, and let it 

 stand for a day. Filter through muslin and squeeze the excess 

 of fluid out of the clot, chop it up and wash with water until 

 aU or nearly all of the colouring substance is removed, place it 

 in 10 times its bulk of 8 p.c. NaCl solution, and warm for one 

 to two days; filter; the filtrate contains fibrin ferment. 



6. Add alcohol in abundance to serum until- no further precipita- 

 tion takes place, filter, and dry the residue over a water-bath 

 at 35' C. ; place the residue in a bottle containing an excess of 

 absolute alcohol, and leave for a month; at the end of this 

 time decant as much alcohol as possible, evaporate the rest 

 at a low temperature (under 40° 0.) ; extract the residue with 

 200 times its volume of water, and filter. The alcohol will 

 have coagulated the greater part of the paraglobulin and albu- 

 min, etc., and so rendered them insoluble in water, hence the 

 aqueous filtrate will contain little else than fibrin ferment, the 

 more so the longer the alcohol has been acting; the compara- 

 tive abeenoe of proteids should be tested by the reactions given 

 in § 16. 

 L. 4 



