This piece appeared as part of the Citation Classics feature. Of his highly cited paper Pontecorvo wrote "I consider it a trivial contribution, though it has had very wide appreciation". On the reverse is a piece by Robert Brown, of the Queensland Department of Primary Industries, who conducted an experiment where he gave 24 students a copy of Pontecorvo's paper Production of indefinitely multiplying mammalian somatic cell hybrids by polyethylene glycol (PEG) treatment and asked for their opinions on what was good or poor and in an attempt to make them think about the factors involved in an editor's decision to accept or reject a paper for publication. Only one student thought the paper should have been published. These extracts were sent to Pontecorvo from"Michael".