While the topics already considered comprise the most important factors in agricultural bacteriology, the farmer's relations to bacteria do not end here. These organisms come incidentally into his life in many ways. They are not always his aids as they are in most of the instances thus far cited. They produce disease in his cattle, as will be noticed in the next chapter. Bacteria are agents of decomposition, and they are just as likely to decompose material which the farmer wishes to preserve as they are to decompose material which the farmer desires to undergo the process of decay. They are as ready to attack his fruits and vegetables as to ripen his cream. The skin of fruits and vegetables is a moderately good protection of the interior from the attack of bacteria; but if the skin be broken in any place, bacteria get in and cause decay, and to prevent it the farmer uses a cold cellar. The bacteria prevent the farmer from preserving meats for any length of time unless he checks their growth in some way. They get into the eggs of his fowls and ruin them. Their troublesome nature in the dairy in preventing the keeping of milk has already been noticed. If he plants his seeds in very moist, damp weather, the soil bacteria cause too rapid a decomposition of the seeds and they rot in the ground instead of sprouting. They produce disagreeable odours, and are the cause of most of the peculiar smells, good and bad, around the barn. They attack the organic matter which gets into his well or brook or pond, decomposing it, filling the water with disagreeable and perhaps poisonous products which render it unfit to drink. They not only aid in the decay of the fallen tree in his forests; but in the same way attack the timber which he wishes to preserve, especially if it is kept in a moist condition. Thus they contribute largely to the gradual destruction of wooden structures. It is therefore the presence of these organisms which forces him to dry his hay, to smoke his hams, to corn his beef, to keep his fruits and vegetables cool and prevent skin bruises, to ice his dairy, to protect his timber from rain, to use stone instead of wooden foundations for buildings, etc. In general, when the farmer desires to get rid of any organic refuse, he depends upon bacteria, for they are his sole agents (aside from fire) for the final destruction of organic matter. When he wishes to convert waste organic refuse into fertilizing material, he uses the bacteria of his compost heap. On the other hand, whenever he desires to preserve organic material, the bacteria are the enemies against which he must carefully guard.