METHODS OF PHYSIOLOGICAL RESEARCH 3 



axiass of ideas that concern phenomena of a secondary nature, 

 because he thinks only of the remote results, constantly observed 

 in daily life, of primary vital phenomena. With him life is 

 characterised by various occu.pations, labours, pleasures, vi^alking, 

 travelling, reading, speaking, eating, drinking, etc., one or another 

 activity appearing as the essential part of his own life according 

 to his vocation and individuality : to one person, life is labour, 

 to another a constant festivity. But the various occupations of 

 daily life are combinations of a few primary vital phenomena. 

 If the development of the conception of life be followed 

 back to early antiquity, when mankind had no presenti- 

 ments of all the occupations that accompany a highly developed 

 culture, when he was unacquainted with fire, when he did not know 

 how to make even the most primitive tools, the conclusion is reached 

 that the conception sprang from the combination of a number of 

 simple phenomena, which early man discovered by self-observation, 

 especially those phenomena that are associated with evident move- 

 ments, such as locomotion, breathing, nutrition, the heart-beat, and 

 others. In fact, it is not difficult to analyse into their primary 

 constituents the complex occupations of our present life, and to 

 recognise that its diversity is produced by various combinations 

 ■of a few elementary phenomena, such as nutrition, respiration, 

 growth, reproduction, movement, and the production of heat. If life 

 be thus conceived as a sum of certain simple phenomena, the task 

 ■of physiology is to determine, investigate, and explain the latter. 



It must be remembered, however, that such a conception of life 

 is limited to the vital phenomena of human beings, while the field 

 of life is far greater. Animals and plants likewise exhibit vital 

 phenomena, and it may be asked whether these latter are the same 

 as or different from the phenomena that prevail among men. It 

 is evident that all living organisms must be included in the 

 .sphere of physiological investigation, the flower and the worm 

 equally with man. Hence the first duty of physiology is to mark 

 out the field of the living, to determine what is living and what 

 is not living — an undertaking that is more difficult than it appears. 

 The conception of life has not always been the same. It 

 has experienced fundamental changes in the course of the develop- 

 ment of the human species. Formed first with respect to man- 

 kind, it was early extended to other objects. With primitive races, 

 the conception was much wider than at present, and they termed 

 living what is no longer regarded as such. With them stars, fire, 

 wind and waves were beings endowed with life and mind, and they 

 were personified in the image of man. The remains of these ideas 

 are still found in the mythology of the classic and modern races. 

 In the course of time the distinction between living and lifeless 

 has been made constantly sharper, but even to-day a child regards 

 ■a steam engine as a living animal. The child is guided more or 



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