THE PHYSICAL PROPERTIES OF THE PROTEINS 19 



latter bodies have been designated " yolk-platelets," and have formed 

 the subject of an exhaustive investigation by Fremy and Valenciennes. 

 They are possibly lecitho-proteins (Walther). Finally may be men- 

 tioned the haemoglobin crystals, which are not observed normally 

 in the animal body, but are occasionally found in preparations, and 

 are sometimes formed as the result of post-mortem changes. 



The first results in the artificial preparation of protein crystals were 

 obtained by Maschke (1859), wno evaporated a saturated solution of 

 aleurone grains from Brazil nuts and obtained tabular, hexagonal 

 crystals. In 1877 Schmiedeberg succeeded in recrystal Using aleu- 

 rone grains, which were also obtained from Brazil nuts. He dissolved 

 the bodies in water at 3O-35 and precipitated them from this 

 solution by means of a current of carbonic acid gas. The precipitate 

 was then redissolved in water at 3O-35 with the addition of an ex- 

 cess of magnesia ; on allowing this solution to evaporate at the same 

 temperature a certain number of large crystals were obtained, which 

 Schmiedeberg regarded as the magnesium compound of the protein. 



The preparation of crystalline proteins from plants formed, during 

 the next two decades, the subject of a large number of memoirs, the 

 chief of which are due to Ritthausen, and to Osborne and his co- 

 workers. The plant globulins, to which class most of these crystalline 

 substances belong, are, it must be recalled, insoluble in water but 

 soluble in salt solutions ; by allowing the proteins to separate from these 

 solutions under suitable conditions the crystalline substances may be 

 obtained. The following method of preparation of edestin, due to 

 Osborne and modified by Leipziger, may serve as an example : 



One kilogram of hemp seed is ground, or pressed in an oil-press 

 (a Buchner press can be employed when available). The remainder of 

 the fat is then removed by extracting with light petroleum. When 

 free from this solvent the seeds are digested at 60 with I litre of 

 5 per cent, salt solution, and the mixture is kept continually stirred. 

 The liquid is then filtered off from the residue through calico and 

 allowed to cool. A precipitate forms and settles at the bottom of 

 the vessel. The supernatant liquid is then decanted off and the 

 precipitate washed by decantation with distilled water. It is then re- 

 dissolved in 500 c.c. of 5 per cent, salt solution, and the solution filtered 

 through a warm filter. On cooling beautiful crystals separate. These 

 are washed with cold 5 per cent, salt solution, distilled water, alcohol 

 and ether. Yield about 100 grams. 



In the cases of plant crystals, substances have been obtained in the 

 laboratory in a crystalline form, which can exist in such form in 

 nature. 



A further great advance was made in 1889, when Hofmeister 

 described the preparation of a crystalline albumin from white of egg ; 

 this was the first instance of the isolation in crystalline form of 

 a protein which was not known to exist in this form in nature. 

 Not long afterwards, Giirber and Michel succeeded in obtaining a 

 crystalline albumin from horse serum. Hofmeister mixed egg-white 

 with an equal volume of saturated ammonium sulphate ; the globulin 

 was thereby precipitated ; on allowing the filtrate from this to 

 evaporate slowly in an open basin, the albumin separated in the form 

 of so-called globulites or spherolites. These were redissolved in dilute 

 ammonium sulphate, and the solution was allowed to slowly evaporate 



