Diseases of the digestive organs are very common among cattle, and may often be traced to defects in feeding. The first three stomachs of the larger ruminants hold the feed for a long time, during which period it is subjected to macerating, mixing, and straining processes in preparation for entrance into the fourth or true stomach. The straining is accomplished through the medium of the manyplies or book, while the paunch, or rumen, with its adjunct, the waterbag, is concerned in the macerating, kneading, and mixing, as well as in regurgitation for rumination or the chewing of the cud. The action of the first three stomachs is merely preparatory to digestion. Thus it would seem that as a result of their complex anatomical and functional arrangement the feed of the ox, when of good quality and wholesome, is in the most favorable condition possible for the digestive process when it reaches the fourth stomach, where true digestion first takes place. The location and arrangement of the stomachs are shown in Plates I and II. If the feed is of improper character, or is so given that it can not be cared for by the animal in a normal way, false fermentations arise, causing indigestion, and possibly, later, organic disease. In feeding cattle there are a number of important considerations apart from the economy of the ration, and some of these are noted below. Feeds must not be damaged by exposure to the weather, by frost, by molds, or by deleterious fermentations. Damaged feeds retard or prevent digestion, and sometimes they contain or cause to be generated substances that irritate the digestive tract, or are distinctly poisonous to the animal. For example, hay that was rained on severely during curing has not only lost a part of its nutritive value through a washing-out process, but what remains is not so readily available as in good hay. Roots that have been frozen are likely to irritate and injure the digestive tract. Grass eaten with frost on it may cause severe indigestion. All moldy feeds are not injurious, for some molds appear to have no influence on the process of digestion, but those of other species may not only retard digestion and cause local injury to the digestive organs, but may cause general poisoning of a severe and fatal type. The following molds have been shown (Dammann) to be dangerous in respect to the production of the morbid conditions enumerated: _Tilletia caries_ grows chiefly in wheat and may be found with the grain, thus appearing in the bran or meal. It causes paralysis of the throat and spinal cord and irritation of the digestive tract. The rusts, such as _Puccinia graminis_, _P. straminis_, _P. Coronata_, and _P. arudinacea_, cause colic and diarrhea, and in some cases partial paralysis of the throat. The rusts that occur on clovers, beans, and peas cause very severe irritation of the lining membrane of the mouth and throat, resulting sometimes in gangrene of this tissue.