At the commencement of the disease, from ten to sixteen days after the introduction of the infectious material, some stiffness in the muscles of the head and neck may be observed. The animal exhibits some difficulty in grasping its food, and in most cases the muscular spasm rapidly increases, and the animal is incapable of moving the head and neck. The jaws are locked or brought forcibly together, the tail is elevated, and the legs are stiff and abducted. In this condition any sudden alarm produces an accession of the spasm, and in the horse a characteristic symptom is the sudden retraction of the eye into its orbit, and the thrusting forward over it of the nictitans membrane (haw). In the acute form of tetanus the spasm is perceived to extend rapidly along the muscles of the back, loin, and tail, and to the muscles of the extremities, which are commonly spread out, and are only moved with difficulty. The respiration is always laboured in consequence of the affection of the respiratory muscles, and the nostrils are widely dilated. The surface of the body is commonly covered with perspiration. The duration of the disease varies, according to the acuteness of the attack, from three or four days to several weeks, but the majority of fatal cases terminate within a week. In cases which recover, the muscular stiffness may continue for several weeks, gradually becoming less until it entirely ceases. Generally it may be said that should the animal survive the ninth day recovery is rendered probable.

Chronic Tetanus is indicated by a less defined spasm, which commonly remains limited to the head and neck; in many cases the animal retains a certain power over the muscles of mastication and can take soft food.