described by Nägeli and others, but it was reserved for Pasteur to show that when a silkworm whose body contained these organisms was pounded up in a mortar with water, and painted over the leaves of the tree upon which healthy worms were fed, all took the disease and died. [Illustration: PLATE IX. AFTER D^R CROOKSHANK _J. T. Balcomb. del._ TYPICAL FORMS OF BACTERIA, SCHIZOMYCETES, OR FISSION-FUNGI.] As the contagious particles were transmitted to the eggs, the method adopted for preventing the spread of the disease was as follows:--Each female moth was kept separate from the others, and allowed to deposit her eggs, and after death her body was crushed up in a mortar as before, and a drop of the fluid examined under the microscope. When any trace of muscadine was found present, the whole of the eggs and body were burnt. In this way the disease was combated, and ultimately stamped out. Pasteur also pointed out that one form or cause of disease must not be confounded with another. For example, muscadine, a true fungus (_Botrytis bassiana_), should not be confounded with another disease known to attack silkworms, termed _pebrin_, this being caused by a bacterium, and, according to the more recent researches of Balbiani, by a Psorospermia. Botrytis is a true mould, belonging to the Oomycetes, and allied to the potato fungus, Peronospora. It is propagated by spores, which, falling on a silkworm, germinate and penetrate its body. A mycelium is then developed, which spreads throughout the body. Hyphæ appear through the skin, and bear white chalky-looking spores; these become detached, and float in the air as an impalpable dust-like smoke. Damp further develops the fungus. Insects suffer much from the ravages of fungi. The house-fly sticking to the window-pane is seen to be surrounded by the mycelia of _Penicillium racemosum_ (_Sporendonema muscæ_, or _Saprolegnia feræ_). In other cases Cordiceps attacks certain caterpillars belonging to the genera Cossus and Hepialus when they are buried in the sand and before their metamorphosis into chrysalides; they are killed by the rapid development of hyphæ and mycelium in their tissues. _Sphæria miletaris_, a parasite of _Bombyx pilyocarpa_, the caterpillar of which is found on pine-trees, is one of the few fungi which may be regarded as beneficial to man, since it aids in the destruction of multitudes of these caterpillars, which otherwise would devour the young shoots and pine needles. Giard specialises other parasites of insects, which he terms Entomophoreæ. Others, _E. rimosa_, attack grasshoppers and the diptera, enveloping them in a dense coating of mycelium and spores, which speedily kills the victim.