054 



THE AMERICAN NATURALIST 



[Vol. XLII 



judicious extension of the concept of stimulus and re- 

 action. 



This effect of zinc upon the growth of mycelium has 

 recently been verified and extended by Javillier, 12 who 

 has made comparative cultures with increasing doses of 

 zinc salt. He grew Sterigmatocystis for four days at 

 34° C. in media with graded additions of zinc salts. As 

 the graphic representation shows, he finds a continuous 



regular increase of the number of grams of final dry 

 weight with doses up to 0.00001 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, abrubtly 

 changing to a level top, suggests, as I have pointed out 

 elsewhere, 13 the cutting-off 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 been at- 

 tained. 



Acceleration of Reaction-velocity by Temperature. 



We now turn to consider the 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 al- 

 most always this effect is very clearly marked. 



Further, the nature of the acceleration is a peculiar 



"Comptes rendu* de 1'Acad. des Sciences, December, 1907. 



"Optima and Limiting Factors. Annals of Botany, Vol. XIX, April, 



