It must not be forgotten that his great contemporaries, Von Helmont and Paracelsus, were not free from many of the curious scientific superstitions of their time, though they had, like him, in many respects the true scientific spirit. Von Helmont, for instance, was a firm believer in the doctrine of spontaneous generation, and even went so far as to consider that it had its application to animals of rather high order. For instance, one of his works contains a rather famous prescription to bring about the spontaneous generation of mice. What was needed was a jar of meal kept in a dark corner covered by some soiled linen. After three weeks these elements {133} would be found to have bred mice. Too much must not be expected, then, of Kircher in the matter of crediting supposedly scientific traditions. It may seem surprising that Father Kircher's book did not produce a greater impression upon the medical research work and teaching of the day and lead to an earlier development of microbiology. Unfortunately, however, the instruments of precision necessary for such a study were not then at hand, and the gradual loss of prestige of the book is therefore readily to be understood. The explanation of this delay in the development of science is very well put by Crookshank, who is the professor of comparative pathology and bacteriology at King's College, London, and one of the acknowledged authorities on these subjects in the medical world. Professor Crookshank says, at the beginning of the first chapter of his text-book on bacteriology, in which he traces the origin of the science, that the first attempt to demonstrate the existence of the _contagium vivum_ dates back almost to the discovery of the microscope:--[Footnote 11] [Footnote 11: _A Text-Book of Bacteriology_. Including the Etiology and Prevention of Infectious Diseases By Edgar M. Crookshank. Fourth Edition London, 1896] Athanasius Kircher nearly two and a half centuries ago expressed his belief that there were definite micro-organisms to which diseases were attributable. The microscope had revealed that all decomposing {134} substances swarmed with countless micro-organisms which were invisible to the naked eye, and Kircher sought for similar organisms in disease, which he considered might be due to their agency. The microscopes which he describes obviously could not admit of the possibility of studying or even detecting the micro-organisms which are now known to be associated with certain diseases; and it is not surprising that his teaching did not at the time gain much attention. They were destined, however, to receive a great impetus from the discoveries which emanated not long after from the father of microscopy, Leeuwenhoek.