12 PROTEIDS. 



with sodium sulphate. Dissolve the precipitate of albumin 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 dry ness at 40. 



According to recent researches egg-albumin may be obtained in a 

 crystalline form 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 1 . 



The primary digestive products obtained during the peptic digestion of egg- 

 albumin have been studied by Chittenden and Bolton 2 . 



2. Serum-albumin. 



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

 serum 3 . Pure solutions of this proteid closely resemble those of egg- 

 albumin in their general reactions, but the difference of the two is 

 clearly shewn by the following statements. 



1. When free from salts and in 1 1'5 p.c. solution it coagulates 

 on heating to 50. The addition of sodium chloride raises the coagulating 

 point to 75 80 4 . Under the conditions in which it occurs in serum 

 it is not found to shew any opalescence on heating at any temperature 

 below 60, and it may be regarded as coagulating completely at 75. 



By fractional heat-coagulation of serum freed from globulin Halliburton 5 has 

 obtained evidence of the existence in the serum of many animals of three albumins 

 coagulating at 7073, 77 78 and 82 85. In some serums only two of these 

 albumins occur. 



2. It is not readily coagulated by alcohol or precipitated by ether : 

 egg-albumin is, and most readily by alcohol. 



3. It is difficult to make any one definite statement as to the 

 specific rotatory power of serum-albumin since it appears to differ for 

 the substance as obtained from different animals. Starke gives it as 

 (a) D = -62-6 for human serum-albumin and - 6O05 for that of the 

 horse. 



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

 xv. Hf. 5 (1891) S. 456. 



2 Stud. Lab. Physiol. Chem. Yale. Univ. Vol. n. (1887), p. 126. 



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

 really of serum-globulin, and this is confirmed by Halliburton, Jl. Physiol. Vol. v. 

 (1883), p. 193. 



4 Starke, loc. cit. S. 18. 



5 Jl. Physiol. Vol. v. 1883, p. 152. But see also Vol. xi. (1890) p. 453. 



