Haemoglobin as a colloid 51 



of dispersity of the substance, the extent to which oxyhaemoglobin 

 will dissociate in the presence of low tensions of oxygen may con- 

 ceivably be largely influenced by this factor. 



Solutions of haemoglobin however finely dispersed will remain 

 colloidal, for the haemoglobin molecule is of such dimensions that it 

 presents surface and itself constitutes a colloidal particle. 



As regards the production of actual visible agglutination or pre- 

 cipitation of haemoglobin by electrolytes, haemoglobin may be said 

 to present the characters of a negatively charged emulsoid or lyophil 

 colloid. It has been shown that a number of negative suspensoid 

 colloids have their electric charge affected, and thus are precipitated, 

 quite as readily by complex trivalent kations (such as Co(NH 3 ) 6 '") as 

 by simple trivalent kations (such as La"', Nd'", &c.), while emulsoids, 

 many of which have their charge affected readily by simple trivalent 

 kations, are almost uninfluenced by complex trivalent kations. The 

 latter is the case with oxyhaemoglobin. A carefully dialysed solution 

 of the pigment is precipitated by a moderate concentration of a salt 

 of lanthanum or cerium (cerous) while no visible effect is produced 

 by the addition of luteo-cobalt chloride even in large concentration. 



Oxyhaemoglobin also shares a property possessed by some sus- 

 pensoids and some emulsoids, namely, extreme sensitiveness towards 

 the hydrogen ion. A low concentration of acid suffices to precipitate 

 oxyhaemoglobin. 



It is to be expected that a change in the hydrogen ion con- 

 centration in the direction of increased acidity, insufficient to cause 

 visible agglutination, will yet cause some aggregation of the molecules 

 of haemoglobin. The fact that gross aggregation is readily obtained 

 by acid lends support to the idea that the effects produced upon the 

 dissociation curves of oxyhaemoglobin by still smaller amounts of 

 acid (Bohr, Barcroft and Orbeli) are due to a minor degree of aggre- 

 gation of the molecules. 



If this hypothesis is a true one, it is to be expected that of 

 the simple kations, exclusive of the hydrogen ion, those of different 

 valency will produce very different effects. Thus a certain small 

 concentration of a salt yielding simple trivalent ions (for instance 

 lanthanum nitrate) will produce an effect on the dissociation curve 

 of oxyhaemoglobin which will be equalled only by a concentration of 

 a magnesium salt some hundreds or perhaps thousands of times as 

 great, while of such salts as NaCl a relatively enormous concentration 

 will be required. Further we should expect to find phosphates and 



42 



