This study analyses the patenting activities of university science and engineering professors in Canada between 1920 and 1975. Unlike most studies on commercial activities in academia, which typically focus on the post-1980 period and on university practices, we focus on the pre-1980 period and on the individual decisions of professors to patent their inventions. Based on quantitative patent data, we show that patenting, and thus professors' interest in the possible commercial value of their scientific discoveries made in university laboratories, was relatively common on an individual and informal basis well before the 1980s and the advent of what is now called "academic capitalism". This contradicts the belief that before that period, universities were a kind of ivory towers in which professors isolated themselves from external influences and engaged only in pure and disinterested research.