The beautiful world of light and splendor, of color and form, is supposed not to be a perception of something which really is. "Through the thick covering of the grape arbor, a ray of sunlight undulates into the cooling shadows. You think you see the ray of light itself, but what you really see is nothing but a flock of dust particles." The truth about light and color is said to be that they are "waves rushing through ether in restless succession at the rate of 160,000 miles per second." This true physical nature of light and color is supposed to be so illusive, that "it required the sharp intellects of the greatest thinkers to reveal to us this true nature of light. We find that every one of our senses is susceptible only to definite external influences, and that the stimulation of different senses produces different conceptions in our mind. Thus the sense organs are the mediators between the external soulless world (undulations of the ether), which is revealed to us by science, and the beautiful world of sense perceptions in which we find ourselves with our minds." Schleiden thus gives an illustration of the fact that there is still a great deal of embarrassment, even in our times, when the understanding of these two worlds is under discussion, that there is still much helpless groping to explain the connection between the world of thought, of knowledge or science, which is in this case represented by undulations of the ether, and between the world of our five senses, represented by the bright and colored lights of the eyes or of reality. At the same time this illustration shows how queer the traditional survivals of speculative philosophy sound in the mouth of a modern scientist. The confused condition of this mode of thought is seen in the distinction between "an external sense-perceived world of science" and another one, "in which we find ourselves with our minds." The distinction between the senses and the mind, between theory and practice, between the special and the general, between truth and error, has been noticed by such thinkers, but they have no solution for it. They know there is something missing, but they do not know where to look for it, and therefore they are confused.