TETANUS. LOCKJAW.--This is an acute infectious disease that is characterized by spasmodic contractions of voluntary muscles. The specific germ remains at the point of infection, and produces toxins that cause tetanic contractions of the muscles. It commonly affects horses, mules, cattle, sheep and swine. The disease is most common in warm, temperate climates. [Illustration: FIG. 108.--Disinfecting boots and coats before leaving a farm where cattle have been inspected for foot-and-mouth disease. (Photographed by S. J. Craig, County Agricultural Agent, Crown Point, Indiana.)] [Illustration: FIG. 109.--Cleaning up and disinfecting premises where an outbreak of foot-and-mouth disease has occurred.] The _specific cause_ is a pin-shaped germ, the _Bacillus tetani_ (Fig. 110), that is present in the soil, especially those that are rich and well manured. The germ enters the body by way of a wound, especially punctured wounds. Infection may take place through some wound in the mucous membrane lining the mouth, or other parts of the digestive tract. Infection may follow a surgical operation, such as castration. In any case, the germ requires an absence of air (oxygen) for its development. _The period of incubation_ varies from one to two weeks, the length of time depending on the nearness of the wound to a large nerve trunk or brain. [Illustration: FIG. 110.--_Bacillus tetani_.] The first _symptom_ observed is a stiffness of the muscles, especially those nearest the point of inoculation or wound. The muscles of the head, neck, back and loins are often affected first, and when pressed upon with the fingers feel hard and rigid. The disease rapidly extends, producing spasms of other muscles of the body. In breathing, the ribs show less movement than normal, the head is held in one position and higher than usual, the ears are stiff or pricked, the nostrils dilated, the lips rigid or drawn back and the eyes retracted, causing the "third eyelid" to protrude over a portion of the eye (Fig. 111). In most cases the muscles of mastication and swallowing are affected. The animal may be unable to open its mouth and swallows with difficulty. When standing, the limbs are spread out so as to increase the base of support, and in acute cases about to terminate fatally, the pulse is quick and small and the respiration shallow, rapid and labored. The animal sweats profusely, falls down and struggles violently, but remains conscious to the end. [Illustration: FIG. 111.--Head of horse affected with tetanus, showing "third eyelid" protruding over the eye.] In the _subacute form_ (Fig. 112) the symptoms are mild, and the animal may be able to move about, eat and drink without very great effort. [Illustration: FIG. 112.--A subacute case of tetanus.]