x] of the Nervous System. 289 



of the properties of muscular tissue, through which he antici- 

 pated modern teaching by nearly a hundred years. In his work 

 on the liver, in discussing how it comes about that the bile is 

 discharged into the intestines at certain times only, namely 

 when it is wanted, he shews that the gall-bladder and biliary 

 duct bring about a greater excretion when they are irritated. 

 And he argues that they cannot be irritated unless they possess 

 the power of being irritated. This power of being irritated he 

 proposes to denote by the term irritability. And he developes 

 this view again in his work on the stomach, Be Ventriculo, 

 published the year of his death, though wholly written as early 

 as 1662, but laid aside in order that he might devote himself to 

 his work De Natura. 



Thus it is undoubtedly to Glisson that we owe the first 

 introduction not only of the word but of the idea of ' irritability,' 

 which, revived by Haller, as we shall immediately see, in the 

 next century, became firmly established in physiology, and has 

 played an important part in the development both of physio- 

 logical and pathological views. Haller used the word in its 

 narrower sense as the property through which muscle responds 

 by movement to an external stimulus ; since then it has been 

 extended to mean response in any way, not by movement or 

 change of form only but by any kind of change, chemical 

 change, change of growth, and the like. And it is worthy of 

 note that Glisson from the very first used the word in its 

 widest sense, distinguishing the various ways in which irrita- 

 bility may be manifested and the various agents by which it 

 may be called forth. 



It was perhaps by reason of the fundamental and highly 

 philosophic character of Glisson's conception that it did not 

 meet with immediate recognition. The idea had to be put 

 forth in the narrower form, which Haller gave to it, in order 

 to be understanded and accepted by physiological people. 



Besides this introduction of the idea of irritability Glisson 

 made another contribution to muscular physiology of a wholly 

 different character, and yet one, from another point of view, of 

 fundamental importance. We have seen that Borelli, with all 

 his zeal for the exact mathematical treatment of physiological 

 p. l. 19 



