By way of summary we must bear in mind that, as regards anatomical conditions, even when depending on the best of sources, we can at present give only fragmentary, incomplete, hypothetical views.
We might have rightly asked whether the physiological states existing along with the working of the creative imagination are the cause, effect, or merely the accompaniment of this activity. Probably all the three conditions are met with. First, concomitance is an accomplished fact, and we may consider it as an organic manifestation parallel to that of the mind. Again, the employment of artificial means to excite and maintain the effervescence of the imagination assigns a causal or antecedent position to the physiologic conditions. Lastly, the psychic activity may be initial and productive of changes in the organism, or, if these already exist, may augment and prolong them.
The most instructive instances are those indicated by very clear manifestations and profound modifications of the bodily condition. Such are the moments of inspiration or simply those of warmth from work which arise in the form of sudden impulses.
The general fact of most importance consists of changes in the blood circulation. Increase of intellectual activity means an increase of work in the cortical cells, dependent on a congested, sometimes a temporarily anæmic state. Hyperæmia seems rather the rule, but we also know that slight anæmia increases cortical excitability. "Weak, contracted pulse; pale, chilly skin; overheated head; brilliant, sunken, roving eyes," such is the classic, frequently quoted description of the physiological state during creative labor. There are numerous inventors who, of their own accord, have noted these changes--irregular pulse, in the case of Lagrange; congestion of the head, in Beethoven, who made use of cold douches to relieve it, etc. This elevation of the vital tone, this nervous tension, translates itself also into motor form through movements analogous to reflexes, without special end, mechanically repeated and always the same in the same man--e.g., movement of the feet, hands, fingers; whittling the table or the arms of a chair (as in the case of Napoleon when he was elaborating a plan of campaign), etc. It is a safety-valve for the excessive flow of nervous impulse, and it is admitted that this method of expenditure is not useless for preserving the understanding in all its clearness. In a word, increase of the cerebral circulation is the formula covering the majority of observations on this subject.