II.
Nutrition—i.e., the essential act of physiological life—is safeguarded by two distinct kinds of tendencies. (I am still speaking of those only which come within the bounds of consciousness, and therefore have a psychological character.) On the one hand, we have the positive tendencies, consisting in an attraction towards and attack on the external world (in this case, food and drink)—viz., hunger and thirst. On the other hand, the negative tendencies consisting in aversion, refusal, flight, and summed up in the state known as disgust.
Disgust is due to excitement of the pneumogastric nerve, producing vomiting, nausea, or mere malaise. This repulsive instinct is connected (1) directly and immediately with taste and smell, two senses which can scarcely be isolated, and whose function is to watch over all substances entering the organism; (2) indirectly and through association of ideas with visual and tactile sensations (sticky, slimy bodies, etc.), by analogy and metaphorically with certain objects which have nothing in common with the nutritive functions—the ugly, the immoral, etc. In virtue of that law of transference or association of analogous sensations, of which we have spoken, the tendency departs more and more from its primary form; but in all cases there is a common groundwork of repulsion, refusal, desire to escape, etc.
Disgust under its primary form (the only one now occupying us) has not been much studied. Writers have contented themselves with classing it among organic sensations, while neglecting its emotional side, i.e., its function in the conservation of the individual. The only work I know on this subject is the excellent monograph of Ch. Richet,[[131]] of which I here give a summary.
Disgust is connected with conservation; it is “an instinctive feeling of protection.” In order to justify this statement, the author passes in review the various objects in nature, noting those which inspire us with disgust, and inquiring into the cause of this. The inorganic kingdom, in general, leaves us indifferent; yet sulphuretted hydrogen, ammonia, and various other gases cause a marked repulsion. This is the effect of an association of ideas; the smell recalls that of decomposition, of a corpse. As regards the vegetable kingdom, the herbivora, by reason of their diet, are the best subjects for observation; their instinct scarcely ever deceives them in the choice of food. We are reminded that, on their arrival in the New World, the Spaniards, hesitating before an unknown flora, whose properties were unknown to them, trusted the judgment of their horses. In man, Richet attributes the repellent influence exerted by bitter aromas to the fact that they frequently co-exist with toxic properties; he takes as types the vegetable alkaloids (quinine, nicotine, etc.), whose power as poisons is in some degree proportioned to their bitterness. So that we have always, at bottom, “the love of life and the horror of death.” In the animal kingdom disgust is aroused by putrescent matter, which indicates or suggests cadaveric decomposition and toxic substances; by parasites, by animals really venomous, or so reputed; for instinct, which sees everything in mass, confounds in the same repugnance the toad and the frog, the venomous serpent and the harmless snake.
In its general bearing, the thesis of the finality of disgust is incontestable. There are, no doubt, many exceptions, many facts difficult to explain (some have been pointed out by Richet); but if we take into account the complexity of the question, all objections fall to the ground.
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.