THE FOKE-BBAIN 



541 



ventricles, where they are bathed by the serous fluid of these 

 cavities. This led him to conclude that this fluid (aqua ventri- 

 culorum cerebri} is the single medium of nervous activity, the 

 sensorium commune, the organ and seat of the soul. 



Sommering dedicated his treatise, Ueber das Organ der Seele, 

 to Kant in order to obtain that great philosopher's opinion upon 

 his hypothesis. Kant's reply is worthy of him, and is of peculiar 

 interest in view of his bent to scepticism. He a priori rejects the 

 idea that the soul, which can only be limited by time, can be 



FIG. 273 6. Internal surface of brain. Cortical areas according to cyto-architecture of grey matter 



in man. (Brodmann.) 



spatially localised. From the physiological point of view only the 

 site of the sensorium commune can be considered, that is, the organ 

 which makes possible " the association of all sensory representa- 

 tions in the mind." This sensorium commune is not the seat of 

 the soul, but it is the immediate organ of the soul, on the one 

 hand isolating the nerves which terminate there so as to keep the 

 sensations distinct, on the other establishing a perfect community 

 between them. Can this sensorium be represented by the water 

 of the cerebral ventricles, as assumed by Sommering ? The great 

 difficulty in admitting this hypothesis is according to Kant 

 that the water, being a fluid, cannot be organised, and without 

 organisation no matter can serve as the immediate organ of the 



