344 Dr. J. W. Pickering. The Chemical and Physiological 



a larger dose, and finally the coagulation of the intravascular blood when 

 the dose is again increased. 



Colloid 7. The colloid 7 is formed by heating together at 130 C. in 

 sealed tubes, for three hours equal weights of alloxan and metamido- 

 benzoic acid, with twice their weight of phosphorus pentoxide. The 

 product of the reaction is a white powder, very slightly soluble in 

 cold water, and sparing soluble in warm water. It should be washed 

 in ice-cold water till the excess of phosphoric acid is removed, and 

 the remaining substance dissolved in concentrated ammonia, The 

 resulting solution is opalescent and straw-coloured, and should be 

 evaporated down at the temperature of the laboratory in vacuo, when 

 a number of translucent, yellowish plates, closely resembling the 

 previously described colloids are formed. These plates are soluble 

 in warm water, and the solution is pale straw-coloured, opalescent, 

 and Isevorotatory (a D = 41) and shows the following reactions: 



Colloid 7. 



It is separated from solution by saturation with either magnesium 

 sulphate, sodium sulphate, sodium chloride, or ammonium sulphate, 

 the colloid rising to the surface of the liquid as a white scum, which 

 redissolves, forming an opalescent solution when thrown into dis- 

 tilled water. It is precipitated by silver nitrate, lead acetate, and 

 mercuric chloride. If the precipitate formed by the addition of lead 

 acetate is suspended in distilled water, and a current of sulphuretted 

 hydrogen is passed through the liquid, the precipitated colloid again 

 passes into solution. 



When heated in the presence of a trace of a neutral salt, fractional 

 heat-coagulation is obtained, which will be detailed in a subsequent 

 section. 



If the colloid 7 is injected into the circulation of dogs or pigmented 

 rabbits, even in large quantities, it does not produce intravascular 

 coagulation, although it somewhat hastens the coagulability of blood 

 withdrawn from the carotid. 



The colloid 7, although yielding many of the chemical reactions that 

 have been used as distinctive tests for proteids, and also behaving in a 

 very similar manner to the previously described proteid-like colloids, does 



