80 PHYSIOLOGY 



solutions differentiates them from the crystalloid substances such 

 as sugar or sodium chloride, under certain conditions it is possible 

 to obtain crystals consisting, largely at any rate, of proteins. Thus 

 in the seeds of certain plants, e.g. hemp seeds, Brazil nut, pumpkin, 

 and castor-oil seeds, the so-called aleurone crystals may be seen 

 under the microscope enclosed in the protoplasm of the cells. These 

 crystals consist of proteins belonging to the class of globulins. By 

 chemical means they can be separated from the surrounding tissues 

 and, after washing, dissolved in a solution of magnesia. Drechsel 

 showed that on dialysing 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 hemoglobin 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 sul- 

 phate 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 increased 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 



