632 



SCIENCE 



[N. 8. Vol. XXVIII. No. 723 



For a while, however, this ideal rate of 

 growth is maintained. At the end of 

 every n minutes there is a doubled amount 

 of protoplasm present, and this will be 

 capable of catalyzing twice the amount of 

 chemical change and carrying on a doubled 

 amount of growth and development. This 

 is what common sense and the law of mass 

 alike indicate, and is exactly what the 

 logarithmic curve expresses. 



This increase of the amount of catalytic 

 protoplasm by its own catalytic activity is 

 an interesting phenomenon. In Section K 

 we call it growth, attribute it to a specific 

 power of protoplasm for assimilation (in 

 the strict sense), and leave it alone as a 

 fundamental phenomenon, but are much 

 concerned as to the distribution of the new 

 growth in innumerable specifically distinct 

 forms. In the chemical section they call 

 this class of phenomenon " autocatalysis, " 

 and a number of cases of it are known. 

 In these a chemical reaction gives rise to 

 some substance which happens to catalyze 

 the particular reaction itself, so that it goes 

 on and on with ever-increasing velocity. 

 Thus, we said that free acid was a catalyst 

 to the hydrolysis of cane-sugar; suppose 

 now that free acid were one of the products 

 of the hydrolysis of sugar, then the 

 catalyst would continually increase in 

 amount in the test-tube, and the reaction 

 would go faster and faster. Under cer- 

 tain conditions this actually happens. 

 Again, when methyl acetate is hydrolyzed 

 we normally get methyl alcohol and free 

 acetic acid. This free acid acts as a 

 catalyst to the hydrolysis, and the rate of 

 change continually accelerates. Here, if 

 the supply of methyl acetate were kept up 

 by constant additions, the reaction would 

 go faster and faster with a logarithmic 

 acceleration. 



For a clear manifestation of this auto- 

 catalytic increase in the plant it is, of 

 course, essential that the supply of food 

 materials to the protoplasm be adequate. 



ACCELERATION OP KEACTION-VELOCITT BY 

 TEMPERATUEE 



We now turn to consider the fourth and 

 last of the principles of chemical me- 

 chanics which we might expect to find 

 manifested in metabolism. 



It is a universal rule that rise of tem- 

 perature 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 been gen- 

 eralized into a rule by van't Hoff. As this 

 increase is repeated for each successive rise 

 of 10° C. either by the same factor or a 

 somewhat smaller one, the acceleration of 

 reaction-velocity by temperature is loga- 

 rithmic in nature, and the curve represent- 

 ing it rises ever more and more steeply. 

 Thus keeping within the vital range of 

 temperature a reaction with a temperature 

 factor of X 2 per 10° C. will go sixteen 

 times as fast at 40° C. as at 0° C, while 

 one with a factor of X 3 will go eighty- 

 one times as fast. 



This general law of the acceleration of 

 reactions by temperature holds equally for 

 reactions which are being accelerated by 

 the presence of catalysts. As we regard 

 the catalyst as merely providing for the 

 particular reaction it catalyzes, a quick 

 way round to the final stage by passing 

 through the intermediate stage of forming 

 a temporary addition-compound with the 

 catalyst itself, so we should expect rise of 

 temperature to accelerate similarly these 

 substituted chemical reactions. 



If this acceleration is a fundamental 



