SERUM ENZYMES 



1 c. c. of serum of typhoid patient diluted to 1-10. 



539 



COLLOIDAL GOLD REACTION 



An important reaction, depending entirely upon the principle of 

 colloidal precipitation, is the so-called colloidal gold reaction exten- 

 sively used for the diagnosis of syphilis of the central nervous sys- 

 tem. In 1901, Zsigmondi, knowing that protein substances will pro- 

 tect various colloids from precipitation by electrolytes, attempted to 

 work out a method by means of which he could quantitatively esti- 

 mate protein in solution by its protective effect. He worked with 

 colloidal metals, using especially colloidal gold. He determined what 

 he called the "Goldzahl" for various proteins, by which he meant the 

 amount in weight of a protein which was just enough to protect from 

 precipitation 10 c.c. of colloidal gold, of a percentage of 0.0053, in 

 the presence of 1 c.c. of 10 per cent. NaCl. It, of course, had long 



