"At a talk I gave at a celebration of the twenty-fifth anniversary of the construction of von Neumann's computer in Princeton a few years ago [i.e., in the early 70's – T.C.] I suddenly started estimating silently in my mind how many theorems are published yearly in mathematical journals. (A theorem being defined as a statement which is just labeled “theorem,” and is published in a recognized mathematical journal.) I made a quick mental calculation, amazing myself that I could do this while talking about something entirely different and came to a number like one hundred thousand theorems per year. Quickly changing the topic I mentioned this and the audience gasped. It may interest the reader that the next day two of the younger mathematicians in the audience came to tell me that impressed by this enormous figure they undertook a more systematic and detailed search in the Institute library. By multiplying the number of journals by the number of yearly issues, by the number of papers per issue and the average number of theorems per paper, their estimate came to nearer two hundred thousand theorems a year. Such an enormous number should certainly give food for thought. If one believes that mathematics is more than games and puzzles, here is something to worry about. Clearly the danger is that mathematics itself will suffer the fate of splitting into different separate sciences, into many independent disciplines tenuously connected. My own hope is that this will not happen, for if the number of theorems is larger than one can possibly survey, who can be trusted to judge what is “important”? The problem becomes one of record keeping, of storage and retrieval of the results obtained. This problem now becomes paramount; one cannot have survival of the fittest if there is no interaction.
It is actually impossible to keep abreast of even the more outstanding and exciting results. How can one reconcile this with the view that mathematics will survive as a single science?" (Ulam, "Adventures of a Mathematician", Ch. 15)

http://www.sfsite.com/04b/sz79.htm