Chemistry fascinated me. The excellent teacher (Goettling) always demonstrated the true connection of the phenomena under consideration; and the theory of chemical affinity took strong hold upon me. Note-taking at these lectures was a thing I never thought of doing; for that which I understood forthwith became a part of me, and that which I failed to understand seemed to me not worth writing down. I have often felt sorry for it since. But as regards this point, I have always had through my whole life the perfectly clear conviction that when I had mastered a whole subject in its intimate relations I could go back upon, and then understand, details which at the time of hearing had been unintelligible to me. In botany I had a clear-sighted, kind-hearted teacher (Batsch). His natural system of botany[20] gave me great satisfaction, although I had always a painful perception of how much still remained for him to classify. However, my view of Nature as one whole became by his means substantially clearer, and my love for the observation of Nature in detail became more animated. I shall always think of him with gratitude. He was also my teacher in natural history. Two principles that he enunciated seized upon me with special force, and seemed to me valid. The first was the conception of the mutual relationship of all animals, extending like a network in all directions; and the second was that the skeleton or bony framework of fishes, birds, and men was one and the same in plan, and that the skeleton of man should be considered as the fundamental type which Nature strove to produce even in the lower forms of creation.[21] I was always highly delighted with his expositions, for they suggested ideas to me which bore fruit both in my intelligence and in my emotional nature. Invariably, whenever I grasped the inter-connection and unity of phenomena, I felt the longings of my spirit and of my soul were fulfilled. I easily understood the other courses I attended, and was able to take a comprehensive glance over the subjects of which they treated. I had seen building going on, and had myself assisted in building, in planting, etc.; here, therefore, I could take notes, and write complete and satisfactory memoranda of the lectures. My stay in Jena had taught me much; by no means so much as it ought to have taught me, but yet I had won for myself a standpoint, both subjective and objective. I could already perceive unity in diversity, the correlation of forces, the interconnection of all living things, life in matter, and the principles of physics and biology.