436 SCIENCE PROGRESS. 



after its downfall, but it serves to illustrate the distinction 

 between the capacity of a tissue for the active state and 

 the readiness with which it enters upon that state. Al- 

 though these two aspects, functional capacity and excita- 

 bility, have been only conceived as distinct through the 

 study of the phenomena of muscle and nerve, it is becoming 

 obvious to all those who have worked upon the subject 

 that the conception of their distinction is probably appli- 

 cable to all living tissues, and thus we are presented with a 

 striking instance of the use of the study of muscle and nerve 

 in enlarging our views upon vital phenomena as a whole. 



Prof. Biedermann treats in his book of other excitable 

 structures possessing definite and easily recognisable excita- 

 tory states besides muscle and nerve ; several chapters are 

 devoted to the electromotive changes, in plants, in epi- 

 thelial cells, in the retina and in electrical organs. 



It would be undesirable to review in any detail the large 

 amount of data which he has compressed into the pages 

 which deal with these subjects ; the subject-matter is some- 

 what complicated and special, but is admirably given, the 

 sole fault which the reader is likely to find being rembarras 

 de richesses owing to the amount of data brought forward. 

 Up to the year of its publication in Germany (1896) the work 

 may be considered as a comprehensive account of the 

 present position of our knowledge. In physiology, as in 

 every growing science, two years implies a considerable 

 extension of previously existing experimental data and the 

 introduction of entirely new points of view to explain the 

 results of recent inquiry. This has been the case with 

 the physiology of the excitable tissues. It would be im- 

 possible in the present article to indicate the many different 

 lines along which advance has taken place during the last 

 year or two. The present writer has therefore selected two 

 instances which his personal knowledge of the subject-matter 

 has led him to regard with special interest, the one being 

 taken from the physiology of muscle and the other from 

 that of nerve. 



The predominant feature of the state of excitation in 

 muscle is undoubtedly the familiar mechanical change which 



