For a concise discussion of this subject the most practical classification is one made on a chronological basis and we may then consider tendinitis as _acute_ and _chronic_. ACUTE TENDINITIS. Etiology and Occurrence.--Causes of tendinitis, as in almost all diseases, may be considered under the heads of predisposing and exciting. Among the predisposing causes of tendinitis may be mentioned, faulty conformation. Everything which has to do with increasing the strain upon tendons adds to the probability of their being over-taxed. Long, sloping, pastern bones; disproportionate development of parts, such as a heavy body and small, weak tendons and long hoofs, are the principal factors which usually predispose to tendinous sprains. Degenerative changes which take place in tendons following constitutional diseases such as influenza may also be classed as a predisposing cause. Excessive strain when put upon tendons in any possible manner, such as is occasioned in running and jumping; making missteps and catching up the weight of the body with one foot, when the force thus thrown upon the supporting structure is great because of momentum gained at a rapid pace, are exciting causes of tendinitis. Symptomatology.--In all cases of acute tendinitis there is presented a characteristic attitude by the subject. Volar flexion in a sufficient degree to relax the inflamed structures is always evident. The foot may be rested on the toe or placed slightly in advance of the one supporting weight, but the fetlock is always thrown forward. More or less swelling of the inflamed tendons is present. Where the deep flexor (perforans) is involved swelling is marked and with swelling there is present the other symptoms of inflammation--heat and supersensitiveness. In manipulating tendons for the purpose of detecting supersensitiveness, care must be taken so that no false conclusion be drawn, because of the aversion many horses have to submitting to palpation of the tendons even when they are in a normal condition. Supporting-leg-lameness is present and varies in degree with the intensity of the pain caused by weight bearing. In many instances, as soon as the subject has traveled a considerable distance, lameness diminishes or discontinues. As soon as the affected animal is permitted to stand long enough to "cool out" there is a return of the lameness, which is then marked. No difficulty is encountered in making a practical diagnosis in tendinitis; that is, one may fail to readily recognize the extent of the involvement as it affects the superficial flexor tendon, for instance, but this has no practical bearing on the prognosis and treatment, when existing inflammation of the deep flexor is recognized. The course of each tendon is readily outlined by palpation; all parts are easily manipulated; and with experience one may readily recognize the extent and degree of the inflammation.