190 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



poison has really acted in some way, and in this case we 

 shall indeed find regulations. 



You may perhaps regard this discussion as a little 

 too academical and hair-splitting, but here again it was 

 for the sake of ensuring a perfectly sound foundation of 

 our chief principles that I undertook it. Very often, indeed, 

 the question has been raised by the defenders of a mechan- 

 istic theory of life, Why then did the organisms not reject all 

 poisons from the very beginning ? We now may reply to 

 that only how could they do so ? How could they "know" 

 what is a poison and what is not, unless they had experienced 

 it ? if we are allowed for a moment to use very anthropo- 

 morphistic language. 



We repeat, therefore, that the functional conditions of 

 the organism must have been actually changed in order 

 that an adaptation may occur. Nothing is more essential 

 to a clear understanding of our problems than to keep 

 fully in mind the exact sense of this definition. 



ON CERTAIN GROUPS OF PRIMARY PHYSIOLOGICAL ADAPTATIONS 



General Remarks on Irritability. Turning now to more 

 special groups of problems concerning physiological adapta- 

 tions, let us begin with the primary class of them, and let 

 us first say a few words on a subject which occasionally 

 has been regarded as the basis of physiological regulation 

 in general. I refer to a most important fact in the general 

 physiology of irritability. Irritability of any kind is known 

 to be re-established, after it has been disturbed by the 

 process of reacting to the stimulus, and in certain cases, 

 in which two different or rather two opposite kinds 



