470 HISTORY OF PHYSIOLOGY. 



Cambridge, who distinguished in the fibres of the 

 muscles of motion a peculiar property, different 

 from any merely mechanical or physical action, 

 His work On the Nature of the Energetic Substance* 

 or on the Life of Nature and of its Three First 

 Faculties, The Perceptive, Appetitive, and Motive, 

 which was published in 1672, is rather metaphysical 

 than physiological. But the principles which he 

 establishes in this treatise he applies more specially 

 to physiology in a treatise On the Stomach and 

 Intestines (Amsterdam, 1677). In this he ascribes 

 to the fibres of the animal body a peculiar power 

 which he calls Irritability. He divides irritation 

 into natural, vital, and animal ; and he points out, 

 though briefly, the gradual differences of irritability 

 in different organs. " It is hardly comprehensible," 

 says Sprengel 13 , "how this lucid and excellent no^ 

 tion of the Cambridge teacher was not accepted 

 with greater alacrity, and further unfolded by his 

 contemporaries." It has, however, since been uni- 

 versally adopted. 



But though the discrimination of muscular irri- 

 tability as a peculiar power, might be a useful step 

 in physiological research, the explanations hitherto 

 offered, of the way in which the nerves operate on 

 this irritability, and discharge their other offices, 

 present only a series of hypotheses. Glisson 14 as- 

 sumed the existence of certain vital spirits, which, 

 according to him, are a mild, sweet fluid, resem- 



13 Spr.iv.47. 14 Ib. iv.38. - 



