pREstDfiNflAL AbbRfisS. 



895 



larger amount than actually suffices should be advantageous. If its function ia 

 catalytic the iron would go on acting indefinitely without being consumed, and 

 so a minute trace might serve to carry out some essential, and even considerable, 

 sub-section of metabolism. 



Elements like manganese, magnesium, and iron are often associated with 

 non-vital catalytic action, and a preparation of iron has recently been quantita- 

 tively investigated which seems to have literally all the properties of an organic 

 oxydase from plant tissues.^ 



As long ago as 1869 Eaulin observed that traces of unessential salts, in 

 particular those of zinc, added to the culture medium in which he grew the 

 fungus Steriymatocystis caused a rapid acceleration of the growth rate. The 

 time that the mycelium took to double its weight was now reduced to a half or 

 even a third. This continued enormous effect of so small a trace of substance is 

 possibly to be regarded as an added catalyst to the normal protoplasmic apparatus. 

 This sort of effect is currently labelled 'chemical stimulation' and has been 

 interpreted as an attempt of the fungus to grow away from an unpleasant 

 environment. To me it looks as if such chemical simulation were really another 

 example of the injudicious extension of the concept of stimulus and reaction. 



This effect of zinc upon the growth of mycelium has recently been verified find 

 extended by Javillier,- who has made comparative cultures wirh increasing doses 

 of zinc salt. He grew Sterir/matocystis for four days at 34° C. in media with 

 graded additions of zinc salts. As the graphic representation shows, he finds a 



Fig. 4. 



continuous regular increase of the number of grammes of final dry weight Avitli 

 do.ses up to OUOOOl per cent,, and then no greater but an equal effect up to 100 

 times as large a dose. 



This form of curve with uniform rise at first, abruptly changing to a level top 

 sugge>ts, as I have pointed out elsewhere,^ the cutting-oft" of the primary rising 

 effect by a limiting factor. In this case presumably the limit set by some other 

 sub-section of the metabolism has teen attained. 



ACCELEBATION OF IlEiCTIOlS'-VELGCITy BY TeMPEKATUEE. 



We now turn to consider t':e fourth and last of the principles of chemical 

 mechanics which we might expect to find manifested in metabolism. 



It is a universal rule that rise of temperature quickens the rate at which a 

 chemical reaction proceeds. Of course in some rare conditions this may not be 

 obvious, but be obscured by superposed secondary causes; but almost always this 

 effect is very clearly marked. 



Further, the nature of the acceleration is a peculiar one. Rise of temperature 

 affects nearly all physical and chemical properties, but none of these is so greatly 

 affected by temperature as is the velocity of chemical reaction. For a rise of 

 10° C. the rate of a reaction is generally increased two or three fold, and this has 



J. Wolff, ' Des puroxyaiastases artificielles,' Comptes rendus de VAcad. des 

 Sciences, June 9, 1908. 



^ Cvmptes rekdtts de VAcad. des Sciences, December 1907. 



' 'Optima and Limiting Factors,' Annals of Botany, vol, xix, April 1905 



