INTRODUCTION XXlll 



tween other substances, by the presence of the catalyzer alone, independently 

 of its chemical affinities and without its being used up in the reaction. A 

 substance is regarded as a catalyzer if it alters the velocity of a chemical reac- 

 tion without itself appearing in the end-products. For instance, if a weak 

 solution of sulphuric acid is allowed to act upon metaUic zinc, the evolution 

 of hydrogen is very slow if both reagents are very pure but the addition of a 

 few drops of platinic chloride is sufficient to cause a stormy evolution of the 

 gas. The reaction proceeds, either in the presence or in the absence of the 

 platinum salt, according to the equation, 



Zn + HjSO*"^ ZnS04 + Hj. 



The platinic salt does not enter into the reaction and so acts simply as a 

 catalyzer. 



Various kinds of catalyzers have now been shown to exist in plants and ani- 

 mals, and these are called ferments' or enzymes. Enzymes, according to Wilhelm 

 Ostwald, are catalyzers formed in the organism during the life of the cell, and 

 it is with their help that the living organism effects most of its chemical processes. 

 Not only are digestion and assimilation regulated entirely by enzymes, but the 

 production of chemical energy by oxidation, at the expense of the oxygen of 

 the air — a process forming the .basis for the life activity of most organisms — 

 is also made possible and directed by these catalyzers. It is well known that 

 oxygen is a very inactive substance at the temperature of organisms and that 

 the maintenance of the life process would be impossible without an acceleration 

 of chemical reaction velocities. Special enzymes (oxydases) are indeed found 

 in plants that act, either within or without the organism, to produce the oxida- 

 tion of various substances at room temperature. 



The attention of scientists was especially attracted by the enzymes of lower 

 plants, such as yeasts and bacteria, these plants having been themselves desig- 

 nated as "organized ferments." The most important discoveries in the physi- 

 ology of yeasts and bacteria are due to Pasteur," who proved the absence of 

 spontaneous generation in the lower organisms, developed a clear conception 

 of the various kinds of fermentation, and devised perfect methods for the con- 

 trol of infectious diseases. The worker in the shop, as well as the farmer in 

 the field, the physician at the bedside, the veterinarian treating domestic ani- 

 mals, the brewer handling his yeast, are all now guided by the ideas of Pasteur. 



A physical discovery that was very important to physiology must here be 

 mentioned, the formulation of the principle of the conservation of energy, by 



' The noun ferment should be dropped, as unnecessary and apt to be misleading. What 

 were once called unorganized ferments are enzymes, and organized ferments (such as yeasts, 

 bacteria, etc.) may be called by name or referred to as fermentation organisms. The word 

 enzyme is frequently mispronounced; it should be pronounced as if spelled enzim, with the 

 first vowel accented and the second short. The spelling enzym is better, but has not come into 

 general use in English. — Ed. 



° Students of chemical physiology should be well acquainted with Pasteur's life and work. 

 See: Vallery-Radot, Ren^, The Lite of Pasteur. Translated by Mrs. R. L. Devonshire. 

 ix -f- 484 p. New York, 1915. — Ed. 



