81 



but they differ physically in at least three respects summarised 

 below. 



TABLE XIV. 



Albumin has a protective action on gold sol while globulin 

 acts almost as if it were a suspensoid. The proportions of albumin 

 and globulin in the various body fluids is practically invariable 

 in health, but during the course of various diseases the balance 

 is upset. If the globulin content is increased relatively to the 

 albumin, then the body fluid will lose a portion of its protective 

 power. In some cases the globulin is not increased, but carries 

 an increased positive electric charge. This increases its precipi- 

 tating action. (Method given in Part II.) 



Evaporation or dehydration, if it reduces the water content 

 below the minimum, will cause coagulation. Conversely, dilution 

 causes a disperse system to break up. 



Heating and Cooling, which alter viscosity directly and also 

 indirectly by altering the amount of water distributed between 

 the two phases, also cause coagulation. Heating certain sols 

 changes them into the more rigid gels. Various native proteins, 

 for instance those of egg white, serum, muscle, coagulate to a 

 gel on heating to a temperature specific for each protein. This 

 process is irreversible and takes place in the presence of electro- 

 lytes. On the other hand, gelatin forms a sol on heating and a 

 gel on cooling a reversible reaction which is profoundly modified 

 by the presence of electrolytes. 



Action of Radium. (See also Chap. XI.) 



The intimate connection between coagulation and the charge 

 carried by the particles is shown by the action of the /? rays of 

 radium. As these rays are negative charges of electricity, they 

 should stabilise negative colloids by increasing their charge, and 

 precipitate positive colloids by neutralising their charge. Hardy 

 found that positively charged acid-globulin was reduced to a 

 state of jelly in three minutes, while the particles of negatively 

 charged alkaline-globulin were rendered more mobile by exposure 

 to (3 radiation. 



