HAEMOGLOBIN 43 



The supernatant liquid is syphoned off, the precipitate washed 

 with water, dissolved in dilute sodium hydroxide (0.05 per cent) 

 and again precipitated with acetic acid. This process is repeated 

 three times, the final precipitate being washed with alcohol and 

 ether and dried over sulphuric acid in an evacuated desiccator. 



The behavior of fibrin strongly resembles that of casein in 

 all stages of its preparation except in its extreme sensitiveness 

 to a slight excess of acid or alkali, for unlike casein, it is readily 

 soluble in weak acetic acid. 



5. Haemoglobin. — The following is the method of prepara- 

 tion recommended by Preyer (26). 



The blood is collected in a vessel and allowed to coagulate 

 and to stand for several hours (or, better, for a day) in a cool 

 place. Then the serum with the white corpuscles and the fat 

 which have collected above the clot is removed and the coag- 

 ulum is washed with distilled water and then cut into very small 

 pieces, and these pieces in turn are repeatedly washed with cold 

 distilled water. Then the clot is comminuted, best by freezing 

 and reducing the frozen mass to powder. This powder is placed 

 in a filter paper and washed with cold distilled water until the 

 filtrate no longer gives any very bulky precipitate with bichloride 

 of mercury. The coagulum is extracted by water heated to from 

 30 to 40 degrees and filtered, and the filtrate is collected in a 

 large cylindrical vessel standing in ice. A small measured portion of 

 the red solution thus obtained is gradually mixed during constant 

 agitation with small quantities of alcohol until a slight precipi- 

 tate forms. This determines how much alcohol may be added to 

 the whole solution without a precipitate appearing. A slightly 

 smaller proportion of alcohol is now added to the remaining 

 filtrate and the mixture is placed in a cooling medium. After a 

 few hours the crystals separate in great abundance. The crys- 

 tals, owing to the large volume of water used, are very easily 

 filtered off in the cold. They are then washed with cold water 

 containing a little alcohol until the filtrate yields only an insig- 

 nificant cloudiness upon the addition of acetate of lead or mer- 

 curic chloride. The product yielded is a very large one. The 

 crystals may be purified by repeated washing by decantation 

 until the wash-water does not become cloudy with bichloride of 

 mercury, lead acetate or silver nitrate. They are then nearly 

 pure, and the ash is free from phosphoric acid and consists of 



