314 PRACTICAL PHYSIOLOGY 



being held inclined slightly upwards. As soon as it is filled place the 

 ends between the jaws of a special spring clip (see Journ. Path, and Bact., 

 16, 1911, 353) which have been prepared with clean plasticine. The 

 clip with the tube is then immersed in water at 35-40 contained in 

 a white basin. The temperature must be kept approximately constant. 

 Not more than ten seconds should elapse between the appearance of 

 the blood and immersion of the tube in the bath. The shot is kept 

 gently rolling from one end of the tube to the other by rotating the 

 handle of the clip. The viscosity increases until the tube has to be 

 held almost vertical to keep the shot travelling. Unless the tube is 

 jerked or knocked, however, the shot should continue to travel smoothly 

 up and down but with diminishing speed till it stops altogether with the 

 tube held vertical. At this point the stop-watch is stopped (it was 

 started as soon as the drop of blood appeared as the result of the prick) 

 and the reading taken. At a temperature of 37 38 C. with this 

 method it was found that for normal individuals the average coagulation 

 time was about one and three-quarter minutes. 



Quantitative Examination of some of the Various Blood Constituents 



Total Nitrogen. Pipette off carefully 1 c.c. of oxalated blood into 

 an ordinary combustion flask and carry out the determination of the 

 total nitrogen present by the ordinary Kjeldahl method as given in the 

 analysis of urine. Or the determination may be carried out after 

 appropriate dilution (1 c.c. oxalated blood diluted to 25 c.c. with water 

 and 1 c.c. of this diluted blood used). 



As regards the determination of the other constituents many methods 

 have been introduced. If a series of determinations have to be carried 

 out on a single blood the method introduced by Folin has been found 

 to be generally useful. The main drawback is the amount of blood 

 required. Folin' s scheme will be given. 



Preparation of Protein-free Blood Filtrates. Collect by means of 

 a syringe or other suitable apparatus, the blood, say 10 c.c., over 

 finely powdered potassium oxalate, using about 20 mg. of oxalate 

 for 10 c.c. blood. Transfer a measured quantity (5 c.c. or more) 

 of oxalated blood to a flask having a capacity of fifteen to twenty 

 times that of the volume of blood taken. Add seven volumes of water 

 to lake the blood, then one volume of a pure 10 per cent, solution of 

 sodium tungstate 1 (Na 2 WO 4 ,2H 2 O) and mix. Add from a graduated 

 pipette, slowly and with shaking, one volume of two-thirds normal 

 sulphuric acid. 2 Close the mouth of the flask with a rubber stopper 

 and shake well. Very few bubbles, if any, will form as the result of the 

 shaking if the conditions are right. Stand for five minutes when the 

 colour of the coagulum ought to change from bright red to dark brown. 

 If this change of colour does not take place, usually due to excess of 

 oxalate, coagulation is incomplete, but coagulation may then be ensured 

 by the addition of 10 per cent, sulphuric acid drop by drop and vigorous 

 snaking after each drop. Continue until practically no foaming and 

 the change to dark brown colour occurs. 



1 Sodium tungstate used should be free from excess of sodium carbonate. 



2 Two-thirds normal H 2 SO 4 , 35 c.c. cone, acid diluted to 1,000 c.c. It is 

 advisable to check by titration. Acid is used to take up the sodium from the 

 tungstate. Tungstic acid combines with the proteins, filtrate is only slightly 

 acid to congo red. 



