In 1853, M. Chas. Robin pointed out the relationship of bacteria to Leptothrix, a form of fungi closely allied to that of mildew; and M. Davaine, in 1868, clearly demonstrated their relationship to the vegetable world. From this time the progress of bacteriological investigation has made rapid strides. Prof. Pasteur in the organisms of fermentation and the role they play therein; Davaine and Hallier in demonstrating the specific relationship of bacteria with charbon or anthrax; and the work of Koch, Nageli, Kohn, Bilroth, Miguel, Burdon, Sanderson, Klein, Weigert, Klebs, Ehrlich, Sternberg, and many others, are too recent to require special mention. Few have more than the faintest conception of the minuteness of these organisms. Prof. Cohn, justifying himself for the unscientific method of comparison which he uses in class instruction by Prof. Tyndall’s argument on the scientific use of the imagination, says he compares man to the cheese mite, as the Strasburg cathedral to a sparrow. Of the animalcules which Leeuwenhoek discovered, they are to man as the bee is to the horse. As improvements have been made in microscopes, just so fast have we penetrated into the world of micro-organisms, until now the proportion between the smallest we can see and man, is as man is to Mont Blanc. Of course, with these exceedingly minute structures, nothing can be made out except points. Among some of the larger forms, a few have been able to see cellia, and in some cases the growth of the spores; but in the present state of microscopical optics the work is slow, and progress in this direction is waiting an advance in the science of optics.