_Season_ is a contributing factor in various ways. Damp seasons sometimes bring the germ to the surface of the soil by the gradual elevation of the water level, or by causing inundations and the deposition of the bacillus on areas of pasture or forage that were previously free, or finally by bringing the earth worms to the surface and leading to the deposition in their casts of the bacillus brought from the infected graves or retentive subsoils. Dry seasons are, however, the anthrax seasons _par excellence_, as they dry up swamps, fens, ponds, lakes, basins, deltas and bottom lands, and render them available for pasture. The germladen mud of these drying lands is also raised in dust and deposited on the vegetation to be taken in by the animals. Again on the drying basins and bottom lands the tempting green vegetation is often pulled up by the roots with adherent, infecting mud. For the above reasons, even in an anthrax region the malady is most prevalent in the late summer and fall, and in certain valleys like those of Corsica the stock is considered safe until the dry autumn weather demands their removal to the mountains. Another reason for the summer epizoötics is found in the transference of the germ by flies. House _flies_, horse-flies, blowflies, mosquitoes, etc., carry the bacillus on their feet, mandibles or piercing apparatus, and even in their stomachs (Bollinger) and transfer it from one individual to another. It is worthy of note that the great majority of cases of local anthrax in man occur on the habitually uncovered parts of the body (face, neck, hands and arms) and start from a centre like the bite of an insect. _Stables_, _stable utensils_, _harness_, _shafts_, _poles_, _fodder_ and _litter_ are familiar bearers of the virus. Butchers’ knives and wagons and surgical instruments are further media of contagion. Certain conditions of the animal system expose it to attack. The fever and constitutional disturbance which are caused by _the extreme heats of summer and autumn_ are strongly predisposing, especially if alternated with frigid nights as seen on the Siberian Steppes. _Privation of water_ raises animal temperature and thus the _drying up of the customary drinking places_ becomes an important factor. _Plethora_ and _starvation_ are alike predisposing, probably by lessening the resisting power of the system. _Overwork_ and _exhaustion_ predispose, as Roger showed by making the immune white rat turn a wheel until worn out and then successfully inoculating it. The addition of lactic acid to the virulent liquid (1:500) greatly encreases its potency (Arloing, Cornevin and Thomas) and the further addition of fermentescible sugar and rest enhances this still more (Kitt). The production of lactic acid by muscular overexertion is thus a potent accessory cause in fatigue.