6 THE POPULAR SCIENCE MONTHLY 



by laymen that " truth " in biology or science in general is of the 

 same order as " truth " in certain of the mental sciences ; that is to 

 say, that everything rests on argument or rhetoric and that what is 

 regarded as true to-day may be expected with some probability to be 

 considered untrue to-morrow. It happens in science, especially in the 

 descriptive sciences like paleontology or zoology, that hypotheses are 

 forwarded, discussed and then abandoned. It should, however, be re- 

 membered that modern biology is fundamentally an experimental and 

 not a descriptive science; and that its results are not rhetorical, but 

 always assume one of two forms: it is either possible to control a life 

 phenomenon to such an extent that we can produce it at desire at any 

 time (as, e. g., the contraction of an excised muscle) ; or we succeed in 

 finding the numerical relation between the conditions of the experiment 

 and the biological result (e. g., Mendel's law of heredity). Biology as 

 far as it is based on these two principles can not retrogress, but must 

 advance. 



2. The Beginning of Scientific Biology 



Scientific biology, defined in this sense, begins with the attempt 

 made by Lavoisier and Laplace (1780) to show that the quantity of 

 heat which is formed in the body of a warm-blooded animal is equal to 

 that formed in a candle, provided that the quantities of carbon dioxide 

 formed in both cases are identical. This was the first attempt to re- 

 duce a life-phenomenon, namely, the formation of animal heat, com- 

 pletely to physico-chemical terms. What these two investigators began 

 with primitive means has been completed by more recent investigators 

 — Pettenkofer and Voit, Eubner and Zuntz. The oxidation of a food- 

 stuff always furnishes the same amount of heat, no matter whether it 

 takes place in the living body or outside. 



These investigations left a gap. The substances which undergo 

 oxidations in the animal body — starch, fat and proteins — are substances 

 which at ordinary temperature are not easily oxidized. They require 

 the temperature of the fiame in order to undergo rapid oxidation 

 through the oxygen of the air. This discrepancy between the oxida- 

 tions in the living body and those in the laboratory manifests itself 

 also in other chemical processes, e. g., digestion or hydrolytic reactions, 

 which were at first found to occur outside the living body rapidly only 

 under conditions incompatible with life. This discrepancy was done 

 away with by the physical chemists, who demonstrated that the same 

 acceleration of chemical reactions which is brought about by a high 

 temperature can also be accomplished at a low temperature with the 

 aid of certain specific substances, the so-called catalyzers. This prog- 

 ress is connected preeminently with the names of Berzelius and Wilhelm 

 Ostwald. The specific substances which accelerate the oxidations at 



