INTERNAL SECRETION AND THE 

 DUCTLESS GLANDS 



CHAPTER I 



INTRODUCTORY-^SECRETION AND INTERNAL SECRETION 



DURING the last quarter of a century a vast amount of 

 investigation has been carried out upon the subject of internal 

 secretion, and very numerous facts have been accumulated 

 and various theories put forward. Our knowledge of the 

 subject is still in many directions very indefinite, and it will 

 be my duty to adopt a somewhat more sceptical and less 

 optimistic attitude in regard to certain branches of the subject 

 than that adopted by some modern writers. It is desirable, 

 at any rate, that the material should be collected and critically 

 examined, though the task is rendered difficult from the fact 

 that many of the contributions are to be found in obscure and 

 even inaccessible publications. 



Before passing on to the discussion of internal secretion, 

 it will be well to define as accurately as possible our conception 

 of secretion in the most general sense of the word. In plants 

 as well as animals, in unicellular as well as in multicellular 

 organisms, various substances are formed as a result of 

 the metabolic activities of the living protoplasm. In the 

 unicellular organisms these substances help in the absorption 

 of food material, or serve some other purpose in the economy 

 of the cell, or they are cast away as waste materials into the 

 medium in which the creature lives. In multicellular organisms 

 the materials may be utilized either in the cell itself or in some 

 other part of the body. In the latter case they may be of 

 service to minister either to the proper function of some special 

 apparatus (such, for example, as the digestive tract), or to the 



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