308 THE COLLOIDAL STATE 



treated with very small traces of hydrocyanic acid was tem- 

 porarily poisoned but recovered after a short time ; a similar 

 effect has also been observed with enzymes. The recovery is 

 probably due to the oxidation of the hydrocyanic acid. 



It was also found that the toxic effect of the hydrocyanic 

 acid was much greater if added directly to the platinum 

 or gold sol than if added to a sol already containing some 

 * hydrogen peroxide. Exactly similar conditions had been 

 previously found by Schonbein* to hold in regard to the 

 addition of hydrocyanic acid and hydrogen peroxide to 

 blood. 



In conclusion, it should be noted that Bredig, while dis- 

 claiming any attempt to trace a fanciful connexion between 

 the colloidal metal solutions and enzymes, emphasizes the fact 

 that the two properties of catalytic action and colloidal nature 

 are common to both classes of compounds and regards the 

 colloidal metals as the simple inorganic analogues of the more 

 complex enzymes. 



One further illustration might be quoted of the chemical 

 activity which is associated with colloidal substances presenting 

 a large surface. A calculation based on the assumption that 

 there are five million red blood corpuscles of diameter -007 mm. 

 contained in I c.mm. of blood reveals the striking fact that 

 the total surface presented by the blood corpuscles contained 

 in 5 litres of blood (the amount contained *in the body of a 

 full grown man) would be about 1875 square metres. From 

 what has gone before it is, therefore, not surprising that these 

 corpuscles should be endowed with special properties enabling 

 them, in the presence of the trace of iron which they contain, 

 to play their part in the highly complex changes involved in 

 respiration. 



* Schonbein: "Zeit. f. Biologic," 1867, 3, 144. 



FURTHER REFERENCES. 



Catalysis. 



Bodlander: "Ueber langsame Verbrennung," " Samml. chem. u. chem- 

 techn. Vortrage," Stuttgart, 1898. 



Bredig: " Kontakt Chemie. u. Lehre v. d. Katalyse u. Enzymwirkung," 

 from " Handbuch d. angew. phys. Chemie," Leipzig, 1905. 



Simon : " La Catalyse," ' Bull. Soc. Chim.," Parishes [3], 29, i-xx. 



