330 CHEMISTRY OF THE PROTEIDS CHAP. 



dividual albumins. The albumins possess, however, the same property 

 as do the amino-acids, namely, that of rotating the light to a different 

 extent according as whether they are free or in salt-like combination ; 

 and a further difficulty is that the salts of the albumins undergo 

 hydrolytic dissociation, and therefore show different rotations according 

 to the concentration of the solution and the nature of the acid or 

 basic radical with which they are combined. 1 As albumins cannot be 

 investigated in strong acids or in alkalies because of their decomposi- 

 tion, only those numbers are available which have been obtained 

 with really pure albumins in perfectly neutral solutions, and such 

 determinations are few. 



Some proteids, e.g. hemoglobin and the nucleo-proteids, are dextro- 

 rotatory, as has been discovered by Gamgee, 2 who also points out 

 various peculiarities of haemoglobin. 



3. Osmotic Pressure 



The question of osmotic pressure has been discussed in a very 

 interesting way by Moore and Parker, 3 who find that a definite osmotic 

 pressure is exerted by colloids in solution. They point out that the 

 albumin-molecule may be considered as built up of a number of 

 smaller molecules, each of which has a comparatively simple structure. 

 These chemically simple molecules, by aggregating, form the physically- 

 complex albumin-molecule, which the authors prefer to call a ' solution- 

 aggregate.' The rise of these aggregates varies within wide limits 

 according to the temperature and chemical reaction of the solution, and 

 as to whether electrolytes are present or absent. The weight of the 

 solution-aggregate is from four to five times greater in serum-albumin 

 than in egg-albumin. In the case of serum - albumin it becomes 

 reduced approximately to one-fifth its value by alkalisation. " Pro- 

 toplasm may be built up by a continuation of such a process of 

 aggregation; absorption of materials by the cell may be governed 

 by the formation of varying aggregations with the protoplasm 

 already built up in the cell, and similarly granule formation in the 

 cell may be produced.' 



Moore and Parker have discussed the investigations of Sebanejew, 4 



1 K. Billow, Pfluger's Arch. f. d. ges. Phys. 58. 207 (1894) ; F. Framm, ibid. 68. 

 144 (1897). 



2 A. Gamgee and Croft Hill, Ber. d. deutsch. c/iem, Ges. 36. I. 913 (1903) ; 

 A. Gamgee and W. Jones, ibid. 36. I. 914 (1903). 



3 B. Moore and W. H. Parker, Amer. Journ. of Physiol. 7. 261 (1902). 



4 Sebanejew, Ber. d. deutsch. chem. Ges. 23. 87 (1890) ; 24. 558 (1891). 



