12 PROTEIDS. 



both these cases the substance is profoundly altered, becoming in 

 the one case acid- in the other alkali-albumin. 



The specific rotatory power, which is stated to be independent 

 of the concentration, is variously given as (a) D = 35'5 (Hoppe- 

 Seyler), or 3779 (Starke). The latter agrees closely with Haas' 

 determination 1 (a) D = 381 and is probably the most correct of 

 the three values. 



Preparations. The fibrous network in white of egg is broken 

 up with scissors and violently agitated in a flask till a thick froth 

 is formed. The flask is then inverted, whereupon the foam rises 

 to the top, carrying the larger part of the fibrous debris with it. 

 The clear subnatant fluid is now carefully drawn off and filtered 

 through fine muslin ; .to this an equal volume of water is added, 

 and the whole is finally filtered through coarse paper. From this 

 point onwards two methods may be employed. 



1. For ordinary purposes the fluid may be very carefully and 

 faintly acidulated with acetic acid, filtered and the filtrate purified 

 by dialysis. 



2. To obtain the purest albumin proceed as follows : 2 Saturate 

 the fluid with magnesium sulphate at 20, filter and saturate the 

 filtrate with sodium sulphate. Dissolve the precipitate of albu- 

 min thus obtained in water and precipitate again with the sodium 

 salt, and after repeating this process several times remove the 

 last traces of salt by dialysis and concentrate to dryness at 40. 



According to recent researches egg-albumin may be obtained in 

 a crystalline^orm by slow evaporation of its solutions in presence 

 of neutral ammonium sulphate. The separation takes place at 

 first in the form of minute spheroidal globules of various sizes, and 

 finally minute needles, either aggregated or separate, make their 

 appearance. It has not as yet been found possible to obtain 

 these so-called crystals from solutions which have been freed 

 by dialysis from the ammonium salt. Further investigation is 

 needed to establish their real nature. 3 



The primary digestive products obtained during the peptic diges- 

 tion of egg-albumin have been studied by Chittendeii and Bolton. 4 



2. Serum-albumin. 



This is the sole proteid. apart from the globulins, which occurs 

 in_sr_um. 5 Pure solutions of this proteid closely resemble those 



1 Pfluger's Arch. Bd. xn. (1876), S. 378. 



2 Starke, loc. cit. 



a Hofmeister, Zt.f. physiol Chem. Bd. xiv. (1889) S. 165. Gabriel, ibid. Bd. xv. 

 Hf. 5 (1891) S. 456. 



4 Stud. Lab. Physiol. Chem. Yale Univ. Vol. u. (1887), p. 126. 



5 'Serum casein ' : of Kiihne and Eichwald was shewn by Hammarsten to consist 



