Such quotations give an insight into the general method and attitude of the Hippocratics. Of an art such as medicine, which even in those times had a long and rational tradition behind it, it is impossible to give more than the merest glimpse in such a review as this. The actual practice is far too complex to set down briefly. This is especially the case with the ancient teaching as regards epidemic disease at which we must cursorily glance. The Hippocratic physicians and indeed all antiquity were as yet ignorant of the nature, and were but dimly aware of the existence, of infection.[85] For them acute disease was something imposed on the patient from outside, but how it reached him from outside and what it was that thus reached him they were still admittedly ignorant. In this dilemma they turned to prolonged observation and noted as a result of repeated experience that epidemic diseases in their world had characteristic seasonal and regional distributions. One country was not quite like another, nor was one season like another nor even one year like another. By a series of carefully collated observations as to how regions, seasons, and years differed from each other, they succeeded in laying the basis of a rational study of epidemiology which gave rise to the notion of an 'epidemic constitution' of the different years, a conception which was very fertile and stimulating to the great clinicians of the seventeenth and eighteenth centuries and is by no means without value even for the modern epidemiologist. The work of the modern fathers of epidemiology was consciously based on Hippocrates. [85] The ancients knew almost nothing of infection _as applied specifically_ to disease. All early peoples--including Greeks and Romans--believed in the transmission of qualities from object to object. Thus purity and impurity and good and bad luck were infections, and diseases were held to be infections in that sense. But there is little evidence in the belief of the special infectivity of _disease as such_ in antiquity. Some few diseases are, however, unequivocally referred to as infectious in a limited number of passages, e. g. ophthalmia, scabies, and phthisis in the περι διαφορας πυρετων {peri diaphoras pyretôn}, _On the differentiae of fevers_, K. vii, p. 279. The references to infection in antiquity are detailed by C. and D. Singer, 'The scientific position of Girolamo Fracastoro', _Annals of Medical History_, vol. i, New York, 1917.