THE PROTEINS ?3 



globulins. By chemical means they can be separated from the surroundin 

 tissues and, after washing, dissolved in a solution of magnesia Drech 

 showed that on dialysmg such a solution against alcohol, the fluid undergoes 

 gradual concentration, and crystalline granules of the magnesia compound 

 of the protein separate out. These crystals contain 1 4 p.c. MgO. A better 

 method of obtaining such crystals has been devised by Osborne The 

 ground seeds are extracted with 10 per cent, sodium chloride solution, and 

 filtered. The filtrate is diluted with water heated to 50 or 60 C. until a 

 slight turbidity forms. After warming the diluted solution until this 

 turbidity disappears, and then allowing it to cool slowly, the protein separates 

 in well-developed crystals. It is possible also to obtain crystals of animal 

 proteins. Haemoglobin, the oxygen-carrying protein of the red blood 

 corpuscles, can be made to crystallise with extreme ease. With some 

 animals, such as the rat, it is only necessary to bring the haemoglobin into 

 solution, by the addition of a little distilled water and ether to the blood, to 

 cause the crystallisation of the liberated haemoglobin. 



Egg albumin and serum albumin may also be crystallised with ease by 

 a method devised by Hofmeister and improved by Hopkins. If, for instance, 

 we wish to crystallise egg albumin, white of eggs is treated with an equal 

 bulk of saturated solution of ammonium sulphate in order to precipitate 

 the globulin. It is then filtered, and the filtrate is treated with 

 saturated ammonium solution until a slight permanent precipitate 

 is produced. This precipitate is then just redissolved by the cautious 

 addition of water, and dilute acetic acid (10 per cent.) is added drop by drop 

 until a slight precipitate is produced. The flask is now corked and allowed 

 to stand for twenty-four hours, when the precipitate, which will have in- 

 creased in quantity, will be found to consist entirely of acicular crystals. A 

 similar method may be used for serum albumin. In each case the crystals 

 contain a considerable proportion of ammonium sulphate. This may be 

 replaced by sodium chloride by washing the crystals with a saturated solution 

 of this salt. By absolute alcohol the crystals may be coagulated and may be 

 then washed practically free from salt, but it is not possible to obtain crystals 

 of coagulable protein free from the presence of some salt. 



Although by repeated crystallisation of egg albumin a product may be 

 obtained which is absolutely constant in both its physical and chemical 

 characters, we cannot ascribe to crystallisation the same importance in 

 securing purity and homogeneity of the substance that we can when we are 

 dealing with inorganic salts. This is due to the fact that these crystals take 

 up other colloids with great ease. When haemoglobin, for instance, is crystal- 

 lised from blood, the first crop of crystals, although thoroughly washed fror 

 their mother liquor, always contain a considerable proportion of i 

 albumin. Indeed, the presence of colloidal material seems to render 

 duction of the so-called mixed crystals much more easy. Thus Schult 

 shown that in urine mixed inorganic crystals can be obtained, 

 urine is allowed to stand twenty-four to forty-eight hours with died 

 phosphate and then filtered. On allowing the filtrate to evaporate slo 



