The famous Peruvian bark was brought to Europe about this time, but it was regarded with extreme suspicion because of its sponsors, and the wildest stories were told of it. Medical treatises teemed with discussions about its properties, some condemning, others commending it. Von Humboldt says: "It almost goes without saying that, among Protestant physicians, hatred of the Jesuits and religious intolerance were at the bottom of the long conflict over the good or evil effected by the drug." The illustrious physician, Bado, gave as his opinion that "it was more precious than all the gold and silver which the Spaniards obtained in South America." It was in 1586, eighteen years after their arrival in Peru, that the work of the Jesuits in Paraguay was inaugurated. Francisco de Victoria, Dominican Bishop of Tucumán had invited them to his diocese, which lay east of the Andes, and his brother in religion, Alonso Guerra, Bishop of Asunción, which was on the Rio de la Plata or Paraná River, also summoned them to his aid, both for the whites and Indians of his flock. They obeyed, and without delay colleges, residences, and retreats for the Spiritual Exercises were instituted in Santiago del Estero, Asunción, Córdoba, Buenos Aires, Corrientes, Tarija, Salta, Tucumán, Santa Fe and elsewhere. These were for the civilized portion of the community, while a new system was devised to save the Indians from their white oppressors. These poor wretches knew the colonists only as slave-dealers and butchers; hence, every attempt to teach them a religion which the whites were alleged to follow was futile. On the other hand, when it was represented to the authorities that Indian slavery had to cease before the natives could be pacified, angry protests were heard on all sides, even from some of the resident priests who maintained that the proper thing for a savage was to be a Spaniard's slave. The missionaries took the matter in their own hands, as they had done in Peru. They went to Spain and applied for royal protection. They obtained what they wanted, so without waiting for the edict to arrive, began their work by plunging into the woods, where cougars, pumas, serpents and savages met them at every step. But this vigorous act only enraged the colonists the more, and the inhuman method of cutting off the missionaries' food-supplies was resorted to in order to force them into submission.