After discussing the partial analyses of identical twins, Petö concludes that 'the results are anything but unambiguous'. Although there was a marked similarity in their obsessional symptoms, their 'psychological attitude, the character traits and the symptoms of disease in spite of the identity of temperament and of external influences, resembled one another neither in their development nor in their more delicate structure nor in their final form'. One is moved to ask whether the partial analyses from which these conclusions on 'the identity … of external influences' were drawn, were not rather macroscopic investigations which failed to reveal microscopic essential differences.