INTRODUCTION 3 



an offshoot from the common trunk of Morphology and Physiology. 

 In so far as it studies the development of forms it is intimately 

 related to morphology ; inasmuch as it investigates the develop- 

 ment of functions it is united by the closest bonds with physiology. 



This threefold development of biology rests on no profound 

 scientific postulate, but merely arises from the convenience of a 

 division of labour, whether in fulfilment of a didactic necessity or in 

 order more rapidly to approach the ideal of a comprehensive know- 

 ledge of living phenomena. We may reasonably anticipate that 

 in proportion as the task assigned to each department approaches its 

 completion, and the corresponding methods of investigation are 

 exhausted, the relations will become more intimate, and the 

 intercourse between the workers in the three several fields more 

 frequent, till finally the great Science of Life, completed by all the 

 achievements of morphology, physiology, psychology, and natural 

 science, is reconstituted in its initial unity, as was predicted by 

 Lazzaro Spallanzani and Johannes Miiller. 



Of late years the special province of Physiology has become 

 so vast that a considerable area of it' is now set apart under the 

 name of Chemical Physiology, and it may seem as though we 

 were still very far from the synthetic reconstitution of Biology 

 as a unitary and well-organised science an ideal image of the 

 living organism. Owing, however, to the aforesaid division of 

 labour, or to the undeniable exhaustion of certain superannuated 

 methods in other directions, General or Comparative Physiology, 

 an important department which was too much neglected in the 

 past, has been developed and perfected ; this comprises the collec- 

 tive study of elementary organisms, in which Cytology and Proto- 

 Morphology present to morphologists and physiologists a common 

 field of research. 



II. In the study of the living organism, the physiologist sets 

 himself three main tasks : to define, to localise, and to interpret the 

 phenomena of life. He aims at 



(a) Definition of vital phenomena : by describing them exactly, 

 forming, if possible, a graphic image that shall be accurate, not 

 merely in its outlines, but also in its minutest details. 



(&) Localisation of the different vital phenomena in the several 

 substrata : by determining the specific energies developed by the 

 various elements, tissues, organs, and systems of which the body is 

 composed. 



(c) Explanation or interpretation of vital phenomena: by in- 

 quiry into their genesis and inner mechanism, investigation of 

 the external or internal conditions on which they depend, deter- 

 mination of the qualitative and quantitative changes they undergo 

 in the play of the said conditions. 



These three tasks represent three different grades of physiological 

 science. The first is purely descriptive; the second, descriptive 



