RATING A THEORY 33 



and gave them fecundity. It took 2000 years 

 for this to happen in the case of the theory of 

 matter and one hundred and fifty years for it to 

 happen in the case of electricity; and no sooner 

 had it happened in the case of both than the 

 two domains hitherto thought of as distinct be- 

 gan to move together and to appear as perhaps 

 but different aspects of one and the same phenom- 

 enon, thus recalling again Thales' ancient be- 

 lief in the essential unity of nature."^ 

 Jacques Loeb asserts: "The epoch-making im- 

 portance of Mendel's work lies in the fact that he, for 

 the first time, gave not a hypothesis, but a theory of 

 heredity, which made it possible to predict the result 

 of hybridization numerically. His work forms the 

 basis for all further work in this field which is of 

 equal theoretical and practical importance."^ 



In the preface to his volume on tropisms Loeb 

 writes: "It is the aim of this monograph to show that 

 the subject of animal conduct can be treated by the 

 quantitative methods of the physicist, and that these 

 methods lead to the forced movements or tropisms 

 theory of animal conduct, which has only recently 

 been carried to some degree of completion."^ 



Concerning the application of quantitative meth- 



* The Electron, second edition, 6. 



• Dynamics of Living Matter, 185. 



' Forced Movements, Tropisms, and Animal Conduct, 7. 



