We may class muscles as _striated_ or _voluntary_ and _unstriated_ or _involuntary._ A third class, _mixed,_ is represented by the heart muscle. The striated is represented by the skeletal muscles, and the unstriated by the thin muscular layers that form part of the wall of the stomach, intestines, bladder and other hollow organs. RHEUMATISM.--This is an inflammation of the tissues that form the locomotory apparatus. The effect of cold on the muscles and tendons is an important factor in its production. It differs from other inflammations by shifting from one part to another. It is termed _muscular rheumatism_ when it affects the muscles, tendons and fascia, and _articular rheumatism_ when it involves the articulations. A second classification, _acute_ and _chronic,_ depends on the character of the inflammation. The muscular form is common in horses, dogs and hogs, while the articular form more commonly affects cattle. _The following causes_ may be considered. Animals that are exposed to cold, wet, changeable weather, or kept in cold, damp, draughty quarters frequently suffer from rheumatism. Under such conditions it is very probable that imperfect metabolism of body tissue occurs, and certain toxic products that are capable of irritating the muscles and articulations form. Clinical symptoms, and the presence of bacteria in the inflamed tissue indicate that bacteria and their toxins play an important part in the development of articular rheumatism. Heredity is said to be an important predisposing factor. One attack always predisposes the animal to a second. _The symptoms vary_ according to the severity of the attack. Local rheumatism is not accompanied by serious symptoms. The regions most commonly involved in local, muscular rheumatism are the shoulder, neck and back. The joints affected in the articular form are the knee, fetlock, hip, elbow and shoulder. The attack is usually sudden and accompanied by fever, more or less loss of appetite and soreness. Loss of control over the movement of the hind parts or walking on the knees may occur in the smaller animals. The larger animals show a slight or severe lameness. The affected muscle or articulation may be swollen, hot and tender. Pressing on the part with the hand or forcing the animal to move about may cause severe pain. Weakness and emaciation may occur in generalized and articular rheumatism, especially if suppuration takes place in the affected joint. _The prognosis_ is more favorable in muscular rheumatism than in the articular form. Both forms may become chronic. It is frequently advisable to destroy animals suffering from the articular form because of their emaciated, weakened condition and the deformed condition of the joints.