Functions of the Cerebrum. 647 



would have done if the brain had been different or absent. But the 

 passage of every stimulus into the brain modifies it, and renders it liable 

 to offer a different reaction against subsequent stimuli. In this respect 

 the central organ may be compared to a bar formed in the bed of a 

 river by the deposit of alluvial matters, which thereafter deflects and 

 arrests the current by which it was created. 



There are two crises in the passage of a stimulation from the external 

 sense organ to a muscle ; the first, when it reaches the brain, arousing 

 sensation and encountering the modif} r ing action of other stimuli ; the 

 second, when the modifications are completed and it reaches the motor 

 nerve on its way to the muscle. It is evident that with many stimuli 

 this second crisis is not immediately reached, and perhaps never, but 

 that the stimulus is neutralized by an opposing one, and reduced to heat, 

 or expends itself in the modification of cells, which thereafter occupy a 

 position of potential energy ready to unwind and exert a modifying in- 

 fluence upon some future action. 



Experiments prove that there are real organs in the cortical cells, en- 

 dowed with the functions of the two crises above mentioned, one set 

 placed at the functional entrance, as it were, and receiving the first on- 

 set of the stimulus, and the stamp and modification which it imposes ; 

 and another set placed at the exit of the stimulus, which leaves upon 

 them its stamp and the index of its motor destination. All incoming 

 stimuli, such as sight, sound, touch, taste, &c. , affect the first class of 

 cells, and when they are destroyed, the memories of these various in- 

 coming sense stimuli are lost. All motor stimuli going out to move a 

 hand or foot, an eye or the tongue, leave their impressions upon cells of 

 the second class, and when such cells are destroyed, the memory of 

 the motor actions registered there, and the ability to repeat them, per- 

 ish with them. They may be termed, respectively, the Initial and Ter- 

 minal organs of the Cortex. The existence of these two sorts of or- 

 gans is ascertained experimentally with a reasonable degree of certainty, 

 and they are such as we might reasonably expect in view of the source 

 and nature of the material energies concerned in their differentiation. 

 Each form of energy modifies a patch of cells in its own peculiar way, 

 and any subsequent stimulation of such cells renews a sensation of that 

 particular kind of energy, as light, sound, contact, &c. Such patches 

 of cells are, respectively, organs of light, sound, contact, &c. These 

 are the organs of the first class. Those others of the second class are 

 organs for and preliminary to muscular motion, but they, as well as the 

 others, are differentiated and operated by the same external energies 

 now transmuted into new forms by their action upon each other in their 

 passage through the ganglions. 



It is obvious that in every advanced brain between the two classes of 



