10 IRRITABILITY 



the question of a law confined to the sense substance, but one 

 that applies to all living substances. Every living substance has 

 its "specific energy," that is, its characteristic vital phenomena 

 and this is produced by stimuli of the most varied kind. This 

 doctrine received an extension of inestimable value for its future 

 development by the great discovery of Schleiden, that the cell is 

 the elementary building stone of the plant organism. Subse- 

 quently Schwann at the instigation of Schleiden made further 

 investigations and found that this discovery applied also to the 

 animal organism. Irritability having been recognized as a general 

 property of living substance, it followed that, after the founda- 

 tion of the cell doctrine, every cell must possess irritability and 

 have its own specific energy. It now became necessary to study 

 the manifestations of irritability of the cells in their specific form. 

 Strange to say, this was done at an earlier date in pathology than 

 in physiology. Indeed, since the time of Brown the study of irri- 

 tability was furthered far more by pathology than by physiology. 

 The chief reason for this is probably the great practical interest 

 that the investigation of disease possesses. Brown having already 

 quite correctly ascribed the existence of disease to the relations 

 of the organism or its parts to stimuli. Rudolph Virchow then, 

 after the establishment of the cell doctrine, arrived at the momen- 

 tous conclusion, that disease must be considered as reactions of 

 the body cells to stimuli. In his epoch-making "Cellular pathol- 

 ogie,"' he has carried out this idea in a classical manner. By irri- 

 tability Virchow understands "a property of the cells, by virtue 

 of which they are set into activity, when affected by external 

 influences." There are, however, various kinds of actions which 

 can be brought about by external influences. But essentially there 

 are three kinds. The effects produced are functional, nutritive, 

 formative. The result of excitation, or if one will, of stimulation 

 of a living part, can, therefore, according to circumstances, be 

 either merely a functional process, or there can be a more or less 

 intense nutritive activity produced without the function being 

 necessarily at the same time activated, or finally, it is possible 



1 Rudolph Virchow: Die Zellularpathologie in ihrer Begriindung auf physiolo- 

 gische und pathologische Gewebelehre. 1 Aufl. Berlin 1858 — 4 Aufl. 1871. 



