Another cause of the paucity of workers in this field is the complexity and difficulty of the subject, which can be handled successfully only by the advanced and mature student. The pre-requisites of competence are an {86} exact philological as well as an archæological training, with a view to the proper appreciation both of texts and monuments; secondly, a general acquaintance with the problems and history of philosophy, and especially of ethics, and with the history of early social institutions and law; thirdly, a comprehensive study of anthropology. To this must be added a sympathetic and minute knowledge of at least two of the great world-religions, whereby alone a critical insight into the essential and significant phenomena of the religious experiences of our race can be obtained. The comparative science of religion has now become possible, thanks partly to the labours of philological specialists in the ancient languages of Europe and Asia, and partly to the organisation of anthropological travel. Let me conclude with remarking that subdivision of labour is imperative in this field: and it is especially in Oxford that the opportunities for the requisite preliminary {87} training are plentiful. It would be a gain for more than science if we could see a group of mature students organised here exploring the various departments of this complex subject in co-operation and with mutual assistance. LECTURE III. THE RITUAL OF PURIFICATION AND THE CONCEPTION OF PURITY: THEIR INFLUENCE ON RELIGION, MORALITY, AND SOCIAL CUSTOM {88} Among all the varied religious acts of man, there is probably none that has been so widely prevalent throughout the different races of mankind as the ritual of purification, nor does any idea seem to have possessed so strong a legislative power in the various departments of our life as the concept of purity. We can trace it back to instincts that we appear to share with the higher animals, and we can track it upwards through the complex rites of the higher religions. The record presents us with a vast mass of phenomena which, as far as I am able to discover, have not yet been reduced to system or unified by any constructive {89} theory of evolution. In this lecture I venture to attempt the systematisation of the subject, first giving a brief summary of the main facts which are well known to the students of primitive anthropology and comparative religion and which confront us in nearly all the societies that have been explored.