3 IRRITABILITY 



To the thinkers both in the field of physiology and medicine of 

 ancient and mediaeval times the conception of irritability was 

 quite foreign. Even a comprehension of the nature of stimuli 

 had not yet begun to crystallize from vague impressions of the 

 various influences of different agents on the human being. 

 Nevertheless they knew of such influences of the most varying 

 kinds upon the human body. The ancients already possessed 

 a materia medica, founded on the real or supposed influence of 

 various mineral, vegetable and animal substances upon the organ- 

 ism. It was also known that heat and cold, light and darkness 

 had an effect upon disease. They likewise believed in the influ- 

 ence of certain factors upon the health of man, which in reality 

 have no effect whatsoever, as the stars and the magnet. But 

 neither in ancient nor in mediaeval times was the state of knowl- 

 edge reached wherein generalizations were made from these 

 agents, which had a real or supposed action upon the organism, 

 and to combine these to a general conception of stimulation. 



The conception of stimulation and irritability cannot however 

 be separated. 



The founder of the doctrine of the irritability of living sub- 

 stance is Francis Glisson (1597-1677), member of the Collegium 

 Medicum in London and at the same time Professor in Cam- 

 bridge. It is a fact also not altogether without interest, that 

 Glisson at the same time was in a certain sense a forerunner of 

 those who interpreted nature from a physical standpoint. Glisson 

 as an anatomist and physiologist was an excellent observer and 

 experimenter, but the most prominent trait of his character 

 was his inclination to philosophic observation and analysis of 

 nature. His "Tractatus de natura substantia energetica"^ must, 

 therefore, be considered as the chief work of his life. In this 

 voluminous book Glisson develops an entire system of natural 

 philosophy, which in accord with the character of the philosophy 

 of that time is unfortunately of an absolutely speculative nature 

 and which had hardly emancipated itself from the scholasticism 



1 Franciscus Clissonius : "Tractatus de natura substantia energetica seu de vita 

 natura ejusque tribus primis facultatibus perceptiva, appetitiva, motiva," etc. Londini 

 M D C L XXII. 



