THE SO-CALLED INOKGANIC ENZYMES 231 



form but in suspended particles, and that to stop the reaction it 

 is only necessary for the hydrocyanic acid to combine with the 

 surface layer of each platinum particle, which may explain the 

 small amount necessary. Such combination might be either of a 

 chemical or physical nature, but the latter is the more probable. 



Before leaving the subject of the action of hydrocyanic acid 

 it may be recalled that it possesses a similar action in minute 

 traces, as shown by Schonbein in the case of the peroxydases accom- 

 panying ferments. Now if these peroxydases are responsible in 

 the tissue cells for the uptake of oxygen by the protoplasm, it 

 may well be that the poisonous action of hydrocyanic acid in 

 such minute doses is due to interference with the action of the 

 peroxydases. 



A large number of other substances were also quantitatively 

 tested byBredig and his co-workers as to their action upon the 

 catalytic power of colloidal platinum. Thus so little as one part 

 of sulphuretted hydrogen in 300,000,000 parts showed clearly a 

 retarding effect upon the catalysis. The colloidal platinum is 

 capable of recovery from the action of some of the reagents em- 

 ployed and not from others. Thus if a stream of air be passed 

 for some time through a solution of colloidal platinum which has 

 been rendered inert by addition of a trace of hydrocyanic acid, 

 so as to remove the latter, the activity is again restored. 



A similar effect is probably found in what has been termed 

 the " oligodynamic " property of heavy metals, as a result of 

 which a trace of certain metals in distilled water, too minute for 

 all chemical analysis, leads to the death of living organisms. 

 Thus mere immersion of a strip of clean copper in a vessel of dis- 

 tilled water containing a number of tadpoles, which would other- 

 wise live therein for weeks, is sufficient to kill the animals in a few 

 hours. 



