124 THE SO-CALLED INORGANIC ENZYMES 



catalysed 50,000 times its own weight of hydrogen and oxygen 

 to water at ordinary temperature without losing its activity in 

 the least. 



The retarding action (or so-called " poisoning " action) of 

 certain substances upon the catalytic action of these inorganic 

 colloidal catalysts is also remarkable upon account of the minute 

 quantities required to stop the reaction. 



For example, the addition of 0-000,000,014 grm. per c.c. of 

 hydrocyanic acid, to the above-mentioned experiment, in which 

 0-000,01 grm. per c.c. of platinum was acting upon 0-06 grm. 

 per c.c. of peroxide, served to decrease the rate of change by one- 

 half, and the addition of 0-000,000,001 grm. per c.c. of hydro- 

 cyanic acid in another experiment had an equal effect upon the 

 velocity of conversion by a colloidal platinum solution in con- 

 centration of 0-000,006 grm. per litre. It is to be noted that 

 the hydrocyanic acid produces its marked effect in amounts of 

 ^io "k TtlcF f t na t of the platinum in these experiments, so that 

 there cannot be an ordinary chemical compound between the 

 catalyst and the " paralysator." It must be remembered, how- 

 ever, that even at these dilutions the platinum is present not in 

 molecular 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 peroxidases accom- 

 panying ferments. Now if these peroxidases 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 

 peroxidases. 



A similar effect is probably found in what has been termed 

 the " oligo-dynamic " 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. 

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

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



