Why do universities have so much learning?

The freshmen bring a little in and the seniors take none out, so [learning] accumulates through the years.
-- A. Lawrence Lowell

From this article by Fred R. Shapiro, author of The Yale Book of Quotations. In the article, he goes into the history behind this and a few other quotes (such as 'Publish or perish', and "Academic politics is so bitter because the stakes are so low").