Please realize that this, as well as all of the other instances in the book, are examples of the stream of consciousness technique that the author uses. In this case, professor Kohler is speaking about Mad Meg's hand. These are simply the thoughts that run through his mind. Let's take a look at the thoughts about Mad Meg, and decipher them a little bit better.
This part of Professor Kohler's thought process is all about hands. It starts out with the hands of Mad Meg, and ends with the hands of Mad Meg. First, there is the idea that Mad Meg's hands have "shaped history." It is then that Professor Kohler's mind wanders. He begins thinking about his own wife, Martha, and about how she wants him to move his study. This continues his thoughts about hands, because moving his study would dirty his hands, and therefore he would have dirt on his pants as a result. (So would Mad Meg if he put his hands on Martha's behind.) Then professor Kohler's thoughts drift back to Mad Meg in regard to hands again. Here, professor Kohler goes into a grand list of all the ways that mad Meg actually used his hands. It is an amazing list of descriptive action words! For example, look at the following (all a description of Mad Meg's hands in action):
misled, lied, latched, locked...explained, expostulated, threatened, wept...joked, jeered, danced, uttered...created, conducted, elicited, ... kneading, molding, tracing, smoothing...
Then, immediately after this extensive description, professor Kohler reverts back to thinking about his own house and how afraid he is in it. Suddenly, professor Koehler is no longer thinking about hands.
In conclusion, the reader can see that this particular part of the book is a perfect example of stream of consciousness technique. Professor Kohler goes from thinking about the hands of a colleague, to his house, back to the extensive description of hands, and back to the fear he feels in his own house. There is no explanation or reasoning to his thoughts. It is a perfect example of stream of consciousness.