What you see when you look at a brain through a microscope is part of your private world. It is the effect in you of a long causal process starting from the brain that you say you are looking at. The brain that you say you are looking at is, no doubt, part of the physical world ; but this is not the brain which is a datum in your experience. That brain is a remote effect of the physical brain.
Source: My Philosophical Development, chap. ２,1959
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