He was not sure whether or not these _corpuscula_ were living, in the sense that they could multiply of themselves. He considered, however, that this was very probable. As to their distribution, he is especially happy in his anticipations of modern medical progress. While he considered it very possible that they were carried through the air, he gives it as his deliberate opinion that living things were the most frequent agents for the distribution of the corpuscles of disease. He is sure that they are carried by flies, for instance, and that they may be inoculated by the stings of such insects as fleas or mosquitoes. He even gives some examples that he knew of in which this was demonstrated. Still more striking is his insistence on the fact that such a contagious disease as pest may be carried by cats and dogs and other domestic animals. The cat seemed to him to be associated with special danger in this matter, and he gives an example of a nunnery which had carefully protected itself against possible infection, but had allowed a cat to come in, with the result that some cases of the disease developed. {130} An interesting bit of discussion is to be found in the chapter in which Father Kircher takes up the consideration of the problem whether infectious disease can ever be produced by the imagination. He is speaking particularly of the pest, but there is more than a suspicion that under the name pest came at times of epidemics many of our modern contagious diseases. Father Kircher says that there is no doubt that worry plays an important role in predisposing persons to take the disease. He does not consider, however, that it can originate of itself, or be engendered in the person without contact with some previous case of pest. With regard to the question of predisposition he is very modern. He points out that many persons do not take the disease, because evidently of some protective quality which they possess. He is sure, too, that the best possible protection comes from keeping in good, general health.