V.] THE BLOOD. 4! 



The blood is heated with 6 to 8 times its volume of water, and slightly 

 acidulated. The filtrate, is evaporated to a small bulk. When a drop of the 

 concentrated filtrate is placed on a slide, cubes of common salt separate out. 



To the colourless filtrate of 23 



(a.) Add silver nitrate = white curdy precipitate soluble in 

 ammonia, but insoluble in nitric acid = chlorides. 



((>.} Add barium chloride = white, heavy precipitate insoluble in 

 nitric acid = sulphates. 



(c.) Add nitric acid and molybdate of ommonium and heat = 

 yellow precipitate = ]>liospliates. 



(d.) Test with Fehling's solution or CuS0 4 and XaHO and boil 

 = red cuprous oxide = reducing sugar, which is glucose. 



ADDITIONAL EXERCISES. 



24. To Obtain Clear Serum. The best way to obtain this is by means of a 

 centrifugal apparatus ; but if the serum contain blood -corpuscles, a fairly 

 clear fluid may be obtained by placing it in a vessel like 



(fig. 17). It consists of the separated top ot a wide flask 

 provided with a cork in the neck, and in the cork is an 

 adjustable tube provided with a clip. When the serum 

 is placed in the apparatus, it must be above the level 

 of the tube. On opening the clip, the clear serum can be 

 drawn off without disturbing the deposit. 



25. Preparation of Serum - Albumin and Serum- 

 Globulin Dilute clear serum with three volumes of a Fl f or 

 saturated solution of neutral ammonium sulphate, and Serum, 

 add crystals of the same salt to complete saturation. 



Filter. The deposit contains the two above-mentioned substances, and is 

 washed with a saturated solution of (NH 4 ). 2 S0 4 . The deposit is then dis- 

 solved in the smallest possible amount of water and dialysed in a parchment 

 tube. In proportion as the salt dialyses, the serum-globulin is deposited as a 

 white powder in the dialysing tube, whilst the serum -albumin remains in 

 solution. It is not difficult to devise an apparatus whereby the water is 

 kept flowing, and even the dialysis tube kept in motion in the running water, 

 provided one has some motor power at hand. (S. Lea, Journal of Physiology, 

 xi. j). 226). 



After complete dialysis the fluid is filtered, the deposited serum -globulin is 

 collected and washed. The filtrate which contains the serum-albumin is 

 carefully neutralised with ammonia, again dialysed, filtered and concentrated 

 at 40" C. After it is cold, the serum-albumin is precipitated at once by strong 

 alcohol, expressed, washed with ether and alcohol, and dried. 



