No. 502] CHE. 



IN LIVING PLANT 635 



change in the last twenty years, a change bringing it more 

 into uniformity with that of the biologist. No longer 

 content with an equation as a final and full expression of 

 a given reaction, the chemist now studies with minutest 

 detail and with quantitative accuracy the progressive 

 stages of development of the reaction 2 and the effect upon 

 it of varied external conditions, of light, temperature, 

 dilution, and the presence of traces of foreign substances. 



Perhaps it is too much to believe that this, as it were 

 physiological, study of each reaction is the effect of some 

 benign irradiation from the biological laboratory. At 

 least, however, it is true that it is the modern study of 

 "slow" chemical reactions wmich has made all this pos- 

 sible, and the living organism consists almost entirely of 

 slow reactions. The earliest studied chemical reactions, 

 those between substances which interact so quickly that no 

 intermediate investigation can be made, did not of course 

 lend themselves to this work, but nowadays wmole classes 

 of reactions are known which are only completed hours 

 or days after the substances are initially mixed. To the 

 slow reactions belong all the hydrolytic and dehydration 

 changes of carbohydrates, fats and proteids that bulk so 

 largely in the metabolism of plants and animals, together 

 with other fermentation changes such as are brought 

 about by oxidases, zymases and enzymes in general. This 

 precise quantitative study of chemical reactions has been 

 developing with remarkable acceleration for some twenty- 

 five years, till it is grown almost into an independent 

 branch of science, physical chemistry. This is sometimes 

 called "general chemistry" because its subject is really 

 the fundamental universal laws of the rate of chemical 

 change, and these laws hold through all the families, gen- 

 era and species of chemical compounds, just as the same 

 physiological laws apply to all the different types of 

 plants. 



