212 Dr. G. Senter. [June 2, 



platinum catalysis of hydrogen peroxide, found that the first-mentioned 

 substance, even in a dilution of 1 gramme-mol. in 7,000,000 litres, 

 reduces the rate of reaction to half its original value. 



I have used in my experiments iodine dissolved in water and also in 

 aqueous solution of potassium iodide. The results are : 



Table XIII. 



Substance used. Constants. 



Iodine dissolved in water, w/4000 O'Ol 16 0-01 60 



m/8000 0-01680-0190 



Iodine, m/40,000, potassium iodide, m/10,000 ... O'OOTO 



Control experiment without iodine 0-0185 



The interesting result is thus obtained that an aqueous solution of 

 iodine exerts only a very slight poisonous action on the enzyme, while 

 a solution in potassium iodide, which contains the iodine in the form of 

 I 3 ions, is distinctly poisonous, though very far behind what Breclig 

 found for the platinum catalysis. Experiments carried out with 

 potassium iodide in 1/10,000 molar solution show that the poisonous 

 effect does not depend upon its presence, since the action was, if 

 anything, accelerated under these conditions. It was observed, how- 

 ever, that the colour of the iodine solution partly disappeared on 

 treatment with H 2 2 , so that some chemical change had evidently taken 

 place. 



Arsenious Oxide. This body is a deadly poison for higher and lower 

 organisms,* but has been found by various investigators to have only 

 a slightly poisonous effect upon enzymes. f This is fully confirmed by 

 the results here given : 



Table XIV. 



Substance used. Constants. 



As 2 3 , w/2000 0-0224 



w/4000 0-0213 



Without As 2 3 0-0214 



From the total number of cubic centimetres of permanganate used, the 

 amount used up by the As 2 3 was subtracted. 



The oxidation of the As 2 3 by hydrogen peroxide is very slow in the 

 dilution here employed, and it was found that this oxidation is not 

 in the least accelerated by the simultaneous decomposition of the 

 hydrogen peroxide. 



Discussion of the Results. 



The Mechanism of the Catalysis by Hcemase.'BetoYe discussing 



generally the results obtained with poisons, the mechanism of the 



* Loew, loc. cit., p. 19. 



t Kobert, loc. cit., p. 153, Buchner, ' Berichte,' vol. 31, p.. 2675. 



I 



