Another of these early workers, writing about the same time, gives a concise account of cheese mites, heading his description “On the creatures which arise in powdery cheese,” he wrote: “The powder examined by means of this instrument (the Compound Microscope) does not present the aspect of dirt, but teems with animalcula. It can be seen that these creatures have claws and talons and are furnished with eyes. The whole surface of their body is beautifully and distinctly coloured in such sort as I have never seen before, and which indeed, cannot be seen without wonder. They may be observed to crawl, eat and work and are equal in apparent size to a man’s nail. Their backs are all spiny and pricked out with various starlike markings and surrounded by a rampart of hairs, all of such marvellous kind that you would say they are a work of art rather than of nature.” At about this period the microscope was used for the first time for medical work and, as far as can be ascertained, Pierre Borel was the first to use it for this purpose, and he learned a great deal about the structure of flesh and the appearance of blood. Of all the early writers on microscopy the man who spread abroad his knowledge of the instrument and its capabilities, more than anyone else, was Kircher, who died in 1680. He was an energetic writer, and wrote on a large number of subjects. His books dealt with magnetism, designs for a calculating machine, light, sound, history of plague, the philosopher’s stone, Egyptian antiquities, a history of China and a grammar. To all who read his book on the plague, it is clear that he had a good idea of infection; he was, in fact, the first writer who suspected it, though the microscope he used could not show him bacteria. In his book he wrote: “Everyone knows that decomposing bodies breed worms, but only since the wonderful discovery of the microscope has it been known that every putrid body swarms with innumerable vermicules, a statement which I should not have believed had I not tested its truth by experiments during many years.” The experiments he performed to prove his statement are so quaint that we give them in his own words. _Experiment I._--“Take a piece of meat which you have exposed by night until the following dawn to the lunar moisture. Then examine it carefully with the smicroscope and you will find the contracted putridity to have been altered by the moon into innumerable wormlets of diverse size, which, however, would escape the sharpness of vision without a good smicroscope. The same is true of cheese, milk, vinegar and similar bodies of a putrifiable nature. The smicroscope, however, must be no ordinary one, but constructed with no less skill than diligence, as is mine which represents objects one thousand times greater than their true size.”