The human being is in the circumstances the most natural transmitting agent. A particular man, on moving from one place to another, will take with him a doctrine, a religion, a germ of opposition or revolt. It may be that he feels conviction about it, like a missionary, an apostle, or a propagandist, but it might also be the case that such an agent remains unconscious of the contagion he spreads, carrying a germ of which he does not suspect either the harmfulness or even the existence: just as there are carriers of non-apparent infections, who know nothing of the virus they harbor, which is undiscovered even by doctors. These are the most dangerous. The carrier who is admitted to be such will preach, harangue, teach, discuss, insinuate, openly sowing the seed along his path, which means that he can be stopped or refuted; but with the unconscious or camouflaged carrier diffusion will be infinitely more insidious: it may be an army soldier in a distant garrison or in the battle-field, a pedlar on his rounds, a laborer recruited for some distant scheme, or even the valet of some millionaire touring round the world. The fantasy, the unpredictability of human contacts are without limit, surpassing the scope of even the wildest imagination. We have only to consider the pollen spread to the uttermost ends of the ancient world by those bees, the Tartar conquerors; the fecundation which those kill-joys, the nomads, periodically brought to the owners of solid hereditary estates; the incessant temptations of neighboring idolatries for the faithful of the true God; or the unforeseen spiritual transports brought about by the Parthians, the Mongols, and the Arabs. The world is infinitely more permeable than one could believe, and in order to be so it has not had to wait for the telephone, the telegraph or the aeroplane to conquer distance and time for us.
We have said that infection may take place through the reading or the hearing of something from a distant source, or through the sight of some image, but, all the same, human intervention will have been necessary: the germ may be laid in a book,. in a screen production, or in a purely formal rite, yet a human intermediary will have been necessary; the source remains inevitably human, for one cannot imagine an idea without a human reservoir, comparable to the germ reservoir in the preservation and transmission of diseases. As far as the virus reservoirs in animals are concerned, however, the comparison stops short, for one can hardly imagine the monkey or the rat playing the part in mind communication that they play in the case of the yellow fever or the plague, even though they be the library rats of the Fable.
The most decisive action is to destroy the germ at its source. But this is often difficult. Either one does not know the germ or, if one knows it, one does not know exactly where to find it. It may be that its possibilities of diffusion have not been properly estimated. It may also be that the germ has multiplied in such a fashion that one is defenseless, tempted to say with the combatent who is completely surrounded: ``They are too many!'' We can well understand the reaction of Simon de Montfort at Béziers in his extermination of the Cathars: ``Kill them all, God will recognize his own!'' The Albigensian germ was in fact completely destroyed, and since then it has only existed in the memory.
Another defense, which is the most usual, consists in suppressing the carrier, or at least in preventing him from penetrating the territory that one wishes to preserve. Thus all the agents of diffusion of this or that doctrine will be systematically destroyed. At all events their entry will be prevented by an impassable barrier at the frontier. That is the traditional Russian system, favored by the Czars long before it was used, as today, by the Soviets. It is also the American system of the immigration quota, which tends to limit the entry of immigrants of Latin or Slav origin, whose influence, it is assumed, might compromise the orthodox Anglo-Saxon tradition. After the First World War America thought that she could in this way keep out a European infection that she considered insidiously Communistic. McCartheyism, after the Second World War, was but a temporary paroxysm of this defensive obsession. If however the infecting agent somehow succeeds in getting in (and how can one really prevent this?) every effort will be made to watch him, to limit his activities and to render him harmless. There may be some doubt as to his degree of harmfulness, and, in this case, he will be subjected to some sort of quarantine. I have been assured that, in the Province of Quebec, the orthodoxy of whose Catholicism is well known, a Canadian student returning from any French university is placed under observation for a certain period, to make sure that no infectious disease develops in him.
The procedure which is most prudent is naturally to take preventive measures: censorship of the press or of books,examination of luggage to make sure that it contains no subversive publication, police supervision of suspects, religious persecution, to say nothing of these so-called ``psychological'' operations of re-education, de-fanaticizing and readapation which are the shame of our century. The Russians and the Chinese are past masters at this type of treatment, but it certainly seems to have been used occasionally in the American army during the Korean war, and it would be most reassuring to know that it is not practised in North Africa. Hitler caused this technique to progress in a truly horrifying way and since then the demoniac progress of neuro-surgery has placed in the hands of experimenters in the matter instruments capable of working miracles in the domain of evil.
One wonders, however, how far such procedures are effective against that winged germ, often invisible, which is the mind. If one ``kills them all,'' as in the case of Albigensian Manicheism,. the enterprise is successful, but if as much as one remains propagation starts again, as is the case with the majority of persecutions: whether it is a case of the Protestants after the revocation of the Edict of Nantes, or the Jews throughout the ages, or of the Armenians assassinated en masse by the Turks, the operation has proved itself useless, for there are still Protestants, Jews and Armenians. The sterilization of the surroundings by the suppression of all contact with the exterior has produced the expected effect in Russia: the state succeeds in preventing the Soviet citizen from knowing what is going on outside, and besides, if any outside propaganda evoked the slightest response this would soon be suppressed by a police force which could, in this context, be described as ``sanitary.'' The iron curtain, and the bamboo curtain, are, from this point of view, as effective a protection as the ancient wall of China, which protected the refined civilization of the Yangtze Kiang against the raids of the Tartar hordes.
So far the comparison between the epidemics of the body and those of the mind has proved fruitful. It remains so as long as the question is one of immunization or vaccination. The laws of nature have given the organism a mechanism for self-defense, corresponding to a fundamental instinct for restoring the balance. That is the significance of immunity, of which vaccination is but a derivative. In the defense measures that human societies adopt against the attacks of propaganda or the penetration of new ideas, immunization and vaccination likewise exist. The virulence of a given doctrine is attenuated by its adapting itself to its surroundings or simply through habit. It can even happen that the injection of a reduced dose can bring with it immunization against a more active form. I seem to have observed several times in Latin America, especially in Argentina, that a particular form of demagogy is the equivalent of a social vaccine against communism. The same thing can be observed in the United States with respect to Irish demagogy, which never goes as far as revolution. A given reform, subtly inspired by the menace itself, will often prevent the disease from declaring itself or at least from spreading when a local infection appears. A healthy society has its own defenses against the infections which might endanger the integrity of its personality. On the other hand an unhealthy society will catch all the illnesses that are going, and will react to all the infections. Rome, in its decline, was not able to defend itself against Christianity. Bismarck said of Russia that she had no business in Europe, and would just catch all its diseases. Freudian psychology spread easily over the Protestant countries, particularly the United States and Switzerland, while Catholic countries put up an effective resistance.
Certain doctrines and certain religions spread like epidemics, following the same lines of least resistance, coming up against the same obstacles, first striking out - depending on the transport available - towards the main centers of communication and distribution, from which they then spread in all directions. Conditions are the same as those we analyzed above with regard to the great pandemics of the nineteenth century, halting places and ports of call being the first to be affected, remote places only being reached after some delay. This explains why certain isolated districts hidden in the mountains or forests escape infection for so long, acting as strongholds of resistance to the infection of progress, and as the last refuge of conservatism.
A typical example of a spiritual epidemic is to be found in the spread of Christianity over the ancient world, which was exceptionally permeable from a spiritual point of view in Roman times. What do we find if we describe this in biological terms? The initial germ is at Jerusalem, but it might have given rise to a merely local infection, limited to the Jewish society in which Christ carried out his apostleship: the apostles, good Jews, who no doubt meant to remain within their own religion, would probably not have spread their faith to any great distance. But there were proselytes among the first Christians, Hellenized Jews or Judaized Greeks, and in their ranks was Stephen, the first martyr. After he had been stoned to death by the fanatics of orthodoxy, his closest disciples, fleeing from Jerusalem, thus fled from the capital to the coasts of Asia Minor, where Jews and Greeks met in the synagogues. Here they were in surroundings which lent themselves admirably to the diffusion of the doctrine which Jerusalem refused to accept, and so, by degrees, Christian centers were constituted in Antioch, Tarsus, Ephesus, Thessalonika and Corinth. The carriers in this instance were the disciples of Stephen, the converted Judaeo-Greeks, the missionary apostles in whose front rank we find Saint Paul, the carrier par excellence through his immense missionary activity. Where the atmosphere was favorable, churches sprang up; where it was not, the Christian seed remained sterile: this was the case at Athens, where the Apostle preached as if in the wilderness. But in other places it was successful, and in the Mediterranean where everything tended towards Rome, it was inevitable that sooner or later the capital of the world should be affected. From Rome the diffusion became generalized and, everything considered, took on for the people of the time, the nature and extent of a pandemic.
The itineraries of Saint Paul are, from this point of view, singularly revealing. The apostle chose the big towns placed along the most frequented lines of communication, because there he found the people less fixed and established, and so more accessible to his preaching; and also because, no doubt, as a tentmaker he found better possibilities there of earning his living. The pattern of roads, the network of sailing routes, obviously also counted for something, for there is a curious mixture of settled plans and irrational impulses in the missionary method. It was natural that he should finally end up in Rome, and, had he not perished under Nero's persecution, doubtless he would have gone on as far as Spain and Gaul. The pressure of East upon West which, in the second and third centuries reached its maximum intensity, meant that all theological developments taking place in Western Asia had an immediate or almost immediate repercussion in Rome, where there were important Asiatic colonies. Maurice Goguel, the great historian of early Christianity, to whom I am indebted for these thoughts on the geography of religion, believed that an exciting study could be made of the geography of primitive Christianity, and the manner in which early Catholicism was built up by a sort of concentration, fusing types of Christianity which at first had differed considerably. The first Christians traveled about a great deal, and their journeys and highly developed practice of hospitality did much to unify them. Christianity thus moved westwards, the center of gravity moving from Jerusalem to Antioch, then to Ephesus, and finally to Rome after a fruitless attempt on the part of Corinth to compete with the capital.
Another example of the geographical extension of a religion can be found at more or less the same time in the spread of the mysteries of Mithras, as appears from the classical research of Franz Cumont. The main Mithraic monuments have been found on the frontiers of the Empire, strung out along, and protected by the Limes. It is clear that the Roman legions were the means of transmission here; it is a case, and a very curious one, of an occupational infection.
We have made use of the same vocabulary to speak of the spread of diseases and of ideas and propaganda: virus, germ, source; carrier, soil, surroundings; contact, contagion, infection, contamination, endemic, epidemic, pandemic; prevention, inoculation, sterilization, immunization, vaccination, quarantine. Surely we have more than a superficial coincidence here: both in the domain of biology and in the world of ideas, certain reactions are shown which are common to all living beings.