One of the difficulties with which scientific endeavour is fraught is that of maintaining detachment. The scientist's interest in his work will lead him to formulate hypotheses and the hypotheses will lead him to expectations about future observations. Is disinterested investigation then possible? Surely the very formulation of a hypothesis engenders a paternal affection and a desire to preserve it. Knowing this, however, the scientist is able to guard against his expectations influencing his observations, defending thus both his objectivity and his honour. But in cases where discriminations are exceptionally difficult to make, then here perhaps, in spite of fore-knowledge of the danger, and in spite of all precautions, an expectation may influence a judgement.