That tastes are not to be argued about is a platitude which has been worn threadbare for centuries past. Taken literally, it would reduce disgust to a purely intellectual manifestation, with no biological bearing; it would deprive it of all specific character, and utterly eliminate it as an instinct. This, however, is a merely superficial position. Contradictions in taste may be compared with contradictions in morality. Variations in manners and customs, according to race, epoch, country, and even caste, do not exclude the existence of a law which has this characteristic common to all cases—that it is derived from the conditions of existence of each group, and is by that right imposed on it. In the same way, disgust exists everywhere, under one form or another, as a protective instinct. The question is complicated, in man, by his intellectual development, and the consequent modification, transformation, or even suppression of this instinct. Between reasoned knowledge and instinctive tendency a battle has been fought, in which the victory inclined sometimes to one side, sometimes to the other. We know the repugnance of animals towards a change of food. The same thing is seen in children, and in the inferior races, when not pressed by necessity. Plasticity grows with civilisation. We may add to this the necessity for new adaptations; thus, in a besieged town, people devour unclean food; the instinct of physiological conservation is a “divided house,” where the positive form struggles against the negative with results, varying in different individuals. To this antagonism between primitive instinct and more complex rational motives let us add the influence of imitation and of fashion, and there will remain few or no unexplained exceptions. As for the _origin_ of this instinct, if we accept the hypothesis of acquired modifications, we may say that the animals and men best fitted for abstaining from hurtful substances, have _ipso facto_ better chances of survival, and that they have been able to transmit to their descendants certain qualities which became fixed and organised as an innate tendency. Whether or not we admit this hypothesis does not matter, our only aim being to remind the reader that disgust is not a capricious and irrelevant phenomenon, but has its roots in the unconscious depths of our organisation. CHAPTER II. FEAR.