6 PROTEIDS. 



silica 1 . The ash of serum-albumin contains an excess of sodium chloride, but the 

 ash of the proteids of muscle contains an excess of potash salts and phosphates. 

 The nature of the connection of the ash with the proteid is still a matter of 

 obscurity, and it is not known whether they constitute an integral part of its 

 molecule or are merely adherent impurities. There is a certain amount of 

 probability that the latter is the case inasmuch as an increasing number of proteids 

 have in recent times been obtained practically free from any ash-residue on ignition. 

 It is however possible that in their natural condition as constituents of the animal 

 tissues and fluids the proteids are combined with salts, the separation of which we 

 are now speaking being an artificial result of the processes employed to effect that 

 separation. The sulphur in proteids is present partly in a stably combined con- 

 dition, partly loosely combined. The latter is removed by boiling with alkalis, the 

 former is not. The proportions of the two differ in the several proteids 2 . 



Proteids met with in the animal body are all amorphous, the only 

 apparent exception being haemoglobin : this substance is however not a 

 pure proteid but a compound of a proteid globin with the less complex 

 haematin. It is to the latter that the power of crystallising is due. 



Some are soluble, some insoluble in water, some are characteristi- 

 cally soluble in moderately concentrated solutions of neutral salts, and 

 all are for the most part insoluble in alcohol and ether ; they are all 

 soluble in strong acids and alkalis, but in becoming dissolved mostly 

 undergo decomposition. Their solutions exert a left-handed rotatory 

 action on the plane of polarisation, the amount depending on various 

 circumstances, and differing for the several proteids. 



Crystals into whose composition certain proteid (globulin) elements largely 

 entered were long since observed in the aleurone-grains of many seeds 3 . Similar 

 crystalloid compounds are also described as occurring occasionally in the egg-yolk 

 of some animals (Amphibia and Fishes). By appropriate methods they may be 

 separated and recrystallized from their solution in distilled water, most readily by 

 Drechsel's method of alcohol dialysis 4 . The crystals consist in no case of pure 

 proteids, but are always compounds of the latter with some inorganic residue such 

 as lime or magnesia. These recrystallized and hence presumably pure compounds 

 haye been frequently analysed with a view to establishing a formula for proteids 

 which should give some clue to their molecular magnitude. An excellent summary 

 of the endeavours to arrive at a definite formula for proteids, based on the above 

 analyses and on those of haemoglobin and certain compounds of egg-albumin with 

 salts of copper and silver is given by Bunge 5 . As the result of these, various 

 formulae have been proposed by the several observers. Very little real importance 



1 Gmelin, Hdbch. d. org. Chem. Bd. vni., S. 285. 



2 A. Kriiger, Pfliiger's Arch. Bd. XLIII. (1888), S. 244. 



3 For literature down to the year 1877, see Weyl, Zt. f. physiol Ch. Bd. i., S. 

 84. See also Hoppe-Seyler's Handbuch, Ed. v. p. 259. Vines, JL of Physiol. 

 Vol. in. (1880), p. 102. Chittenden and Hartwell, JL of Physiol. Vol. xi. (1890), 

 p. 435. 



4 Jl.f. praU. Chem. N.F. Bd. xix. (1879), S. 331. 



5 Lehrb. d. physiol. u. path. Chem. 1887, Sn. 52-58. For most recent analysis 

 of haemoglobin from dog's blood see Jaquet, Zt. f. physiol. Ch. Bd. xn. (1888), S. 

 285, xiv. S. 289. Chittenden and Whitehouse, Stud. Lab. physiol. Chem. Yale, Vol. 

 ii. (1887), p. 95. 



