6 INTRODUCTION 



peculiar manifestation of energy 1 . He who considers our inability to grasp 

 the essential nature of the vital mechanism to be sufficient ground for as- 

 suming the existence of a special vital force, must also permit the aboriginal 

 Australian to endow with magical powers the musical-box or the watch 

 which is totally incomprehensible to him. An intelligent person could 

 without difficulty ultimately gain a clear comprehension of the mechanism 

 of a musical-box or watch, and of the causes determining the particular 

 performance of which it is capable, although it might be quite impossible 

 for him to create such a mechanism, or to procure an historical account 

 of its discovery and perfection. This example may suffice to point out 

 the relationship of biological investigations to the phenomena which they are 

 required to explain. Moreover, since we can only guess at the evolutionary 

 history of the organism, it is only possible for us to deal with the physio- 

 logical and other properties which it now possesses, and however clearly 

 we may be able to explain the peculiarities of a given plant, as being 

 due to characters and tendencies inherited from its parents, we shall still 

 be unable to determine with certainty the evolutionary origin of that 

 particular species. 



In their respective aims and principles, all sciences meet on common 

 ground. When we bear in mind the fact that the division of science into 

 separate subjects is due merely to a convenient mental abstraction, it is easy 

 to realize how worthless is any discussion as to whether Physiology and 

 Astronomy are, for instance, subordinate to, or co-ordinate with, Physics and 

 Chemistry. Each of these subdivisions of science has an equal right to 

 claim independence. Physiology has, more especially, as its ultimate aim, the 

 investigation of the meaning of the elements and .forces which are at the 

 disposal of the living organism and their importance in maintaining its vital 

 activities. This is probably the most difficult and complicated problem 

 which the progress of creation on our earth has given us to solve. It is 

 hardly necessary to point out that no fruitful investigation into the wonderful 

 mechanism of the living organism is possible without a careful study of the 

 simpler relations presented to us, and without the powerful support of 

 Chemistry and Physics. 



The chemists and physicists of a hundred years ago had not, and could 

 not have had, the least idea of the telephone or of the various aniline dyes 

 and the various uses to which these have been put during the present 

 century. It is in the same way equally certain that our present knowledge 

 of Physics, Chemistry, and other sciences is insufficient to enable us to 

 realize all the permutations and combinations of the elementary forces and 

 substances which are possible in the living organism, or the very varied 



1 On Vital Force see Lotze, Wagner's Handworterbuch der Physiologic, 1842, Bd. I ; du Bois- 

 Raymond, Reden, 1867, Bd. n, p. i. 



