A large number of animals "enjoy" light but only a small number of them are so "fascinated" by light that they cannot resist a "craving" to fly toward a light, contact with which may mean death to them. Only that small minority can be called in scientific jargon "positively phototropic," in sentimental parlance "hopelessly in love" with light.
All animals are affected in some fashion by an electric current passing thru their bodies, but only a minority of them are so affected by it that they must, whether they wish it or not, face the positive electrode, as a lover fascinated by the face of his sweetheart. Only these can be characterised as "positively galvanotropic."
Erotropism.Likewise a hundred men may be charmed by the sight of a woman. Only one or two from their number may feel compelled to seek complete union with her regardless of the obstacles to be surmounted, of the criticism their actions may arouse, of the expenditure of time, money and energy the adventure may entail. Only this minority may be considered as "positively erotropic."
In other words it is the primal compulsion which nature uses to assure the continuance of the race and which I might designate as "erotropism" which must be considered the basis for a discussion of love.
Love as commonly understood or misunderstood at the present day, is a series of variations on the theme of erotropism, variations due to the complication of modern civilisation and the restrictions placed upon all biological phenomena by the necessities of life in communities.
What is the Heart? The reader will notice that I have thus far avoided any mention of the "heart" altho that organ is commonly identified with the various emotions of love.
Physiologically speaking, the heart is no more vitally concerned with love than with any other disturbing feeling and emotion. Love may at times cause our heart to beat wildly, but so does strong coffee, so does acute indigestion, so does blood poisoning, so does any sort of violent fear.
The heart, we must not forget, is a mere muscle, which is no more capable of being the seat of an emotion than our biceps or our calves.