viii PREFACE. 



anatomy and physiology and to practical medicine, and 

 that I have not always been consistent in the extent of 

 these references. The attentive reader will however dis- 

 cover, I trust, that I have proceeded with great deliberation, 

 and that if in certain cases I have made greater digressions 

 into the provinces of the cognate sciences than in others, 

 it has been because I considered that I was called upon to 

 do so in the interest of the particular subject, and therefore 

 in the interest of the reader. Thus, in the chapter on the 

 ' Contractile Tissues' the histological descriptions are far more 

 detailed and the general review of known physiological facts 

 much more complete than in the case of the nervous tissues, 

 and the reason is obvious. It would have been unsatis- 

 factory to discuss the chemical processes of muscle without 

 considering, in some cases in considerable detail, the results 

 of the work of the histologist and of the experimental 

 physiologist. On the other hand, in dealing with the 

 scanty facts yet known to us concerning the chemical 

 history of the nervous tissues, only the barest outline of 

 the histology of the nervous system is essential. 



Although this volume, in the main, deals with the 

 chemistry of the elementary tissues and not with the 

 processes which are characteristic of the complex organs of 

 the body, for the sake of convenience some exceptions have 

 been made. Thus the chemistry of the organs of sense 

 has been made to follow the chapter on the chemistry of the 

 nervous tissues, because this seemed the most convenient 

 place for introducing a systematic account of any facts 

 relating to them. 



It has been a constant object with me to give the reader 

 a very full and, so far as possible, independent account of 

 the state of knowledge on the subjects discussed, and I trust 



