Based on this notion of constant danger from infection, there arose a code of unwritten custom as rigid as that enforced by a careful physician in infectious cases at the present day; and thus, too, in course of time there was developed the idea of the possibility of _disinfection_, an idea as salutary as the discovery in medical science of effective methods for the disinfection of disease. The code of taboo had an obvious ethical value, as Dr. Jevons pointed out long ago;[28] like all discipline carried out with a social end in view, it helped men to realise that they were under obligations to the community of which they were a part, and that they would be visited by severe penalties if they neglected these duties. But it inevitably tended to forge a set of fetters binding and cramping the minds of its captives with a countless number of terrors; life was full of constant anxiety, of that feeling expressed by the later Romans in the word _religio_,[29] which, as we shall see, probably had its origin in this period of primitive superstition. The only remedy is the _discovery of the means of disinfection_, or, as we commonly call it, of _purification_: a discovery which must have been going on for ages, and only finds its completion at Rome in the era of the City-state. We shall return to this part of the subject when we deal with the ritual of purification; at present we must attend to certain survivals in that ritual which suggest that at one time the ancestors of the Roman people lived under this unwritten code of taboo.