Researches in the Theory and Calculus of Operations. 317 



the ventilated blood is restored to the left division of the 

 heart, for renewed distribution in the course previously 

 detailed; and this constitutes a second general cireuit. 

 Minor subsidiary circuits are deferred for consideration in 

 another place, with one important exception. The internal 

 carotid arteries supply the brain with the sanguiferous 

 fluid, the refuse portions of which is returned whence it 

 came by the internal jugular veins. Like the galvanic ap- 

 paratus, the cerebrum eliminates nervous force from the 

 fluids it receives ; in which operation, the grey and the 

 white portions of the substance take the task respectively 

 of the zinc and copper of the galvanic jar. When brought 

 into energetic action by sensational disturbance transmitted 

 from the thalamus and associated centres of the sensations 

 received from without, the resultant force evolved by cere- 

 bral decomposition is collected on the cerebellum as re- 

 ceiver (or prime conductor), whence its direction in the 

 efferent nerves is determined by the message coming on 

 the afferent nerves to the central sensorium, so as to ini- 

 tiate muscular reaction upon the circumferential points 

 where the disturbance commenced. But in a state of com- 

 parative calm, the action may be merely sufficient to keep 

 up the play of attention to the passing sensuous impres- 

 sions. A muscle grasps and relaxes, the heart and arteries 

 contract to expel and expand to receive, the digestive organs 

 turn and return in peristaltic movement, etc. ; all these are 

 alternations of exertion and repose, of labor and rest, waves 

 in which the oscillations are ceaseless in life but short in 

 periods of time. The organs of sensation and thought also 

 have their periods of alternate labor and repose, dictated 

 normally by the presence and withdrawal of the light of 

 day. The successive vibratory periods of sensorial thought 

 in dreams sometimes approach the state of continuity ; 

 while in wakeful moments, thought, when under the com- 

 mand of volition, may be prolonged to a much larger than 



