4 IRRITABILITY 



to transfer his meaning into our present methods of thought. 

 This distinction would then simply point out the different means 

 by which the stimuli can reach the irritable structures. The "Per- 

 ceptio naturalis" is that which today we should call "direct 

 response" to stimulation, that is, the excitation of the fiber by 

 artificial stimuli applied directly to the tissue. Glisson shows 

 here, that the intestines and muscles in the body immediately 

 after death and even when removed from the body can be 

 stimulated to movement by means of corrosive fluids or cold. 

 The "Perceptio sensitiva" is, according to Glisson, the excitation 

 of the fibers by external stimuli which act on the intact body as 

 a whole by way of the sensory nerves. The "Perceptio ah appe- 

 titu animali regulate" finally is the excitation by inner stimuli 

 proceeding from the brain. The Perceptio naturalis is possessed 

 by all parts of the body, even the fluids, the bones and the fat. 

 All of them are irritable. But a "vitale" and a special "animal" 

 irritability they do not possess to a perceptible degree. These 

 forms of irritability belong only to the special parts of the body. 

 Here, however, the distinctions made by Glisson are quite vague 

 and contradictory. In his "Tractatus de ventriculo et intestinis" 

 Glisson sharply distinguishes the "sensatio" from the "perceptio." 

 The perceptio in itself is not a sensation, for although individual 

 organs of the body are irritable, as they all possess a "perceptio," 

 they are not in themselves sensitive. The "sensatio," the sensa- 

 tion, only arises when the external "perceptio" of the individual 

 organs combine through the nerves with the internal "perceptio" 

 of the brain. "Nisi enim percepto externa ab interna simul per- 

 cipiatur, non est cognitio sensitiva completa." Sensitivity is, 

 therefore, a special faculty, that is only based upon irritability. 

 I have treated the views of Glisson somewhat in detail for 

 on the one hand this seemed to me to be only due to the founder 

 of the doctrine of irritability, and on the other we have 

 here for the first time, although in somewhat vague and little 

 worked out form, the discovery of a general property of all 

 living substance, and its fundamental importance for the life 

 of the organisms. One might, therefore, in a certain sense, date 

 from Glisson the beginning of general physiology, and all the 



