Rabies is widely distributed, being most prevalent in the temperate zone, and where the population is most dense. It has been excluded from Australia, Tasmania and New Zealand by a rigid inspection and quarantine of all imported dogs. _The specific cause of rabies_ is probably a protozoan parasite (the Negri bodies present in nerve-cells, Fig. 105). The germ spreads from the wounds through the nerves and central nervous system. The disease-producing organisms are present in great numbers in the nerve-tissue and saliva. _The period of incubation_ varies from a few days to several months. It is usually from ten to seventy days. _The symptoms_ differ in the different species. There are two forms of the disease: the _furious_ and the _dumb_. The former is more common. [Illustration: FIG. 105.--Negri bodies in nerve-tissue.] _In the dog, the symptoms may be divided into three stages_. The first, or _melancholy stage_, usually lasts from twelve to forty-eight hours. The animal's behavior is altered and it becomes sullen, irritable and nervous. Sometimes it is friendly and inclined to lick the hand of its master. An inclination to gnaw or swallow indigestible objects is sometimes noted. Frequently a certain part of the skin is rubbed or licked. The second, or _furious stage_, may last several days. Violent nervous or rabid symptoms are manifested, and the dog may leave home and travel long distances. The animal usually shows a strong inclination to bite. It may move about snapping at imaginary objects in its delirium, and may bite any person or animal with which it comes in contact. The bark is peculiar, the appetite is lost and the animal becomes weak and emaciated. In the third, or _paralytic stage_, the dog may present an emaciated, dirty, ragged appearance. The lower jaw may drop, the tongue hangs from the lips and the eyes appear sunken and glassy. Paralysis of the hind parts may be present. _In the dumb form_, the paralytic symptoms predominate and the disease pursues a short course. Rabies terminates in death in from four to ten days. _Furious rabies_ is more common in the _horse_. The animal is very nervous, restless and alert. It may attack other animals in a vicious manner, kicking and biting them. The animal does not seem to care to eat or drink, and usually shows violent nervous symptoms, such as biting the manger, rearing and kicking when confined in the stable. _Cattle_ butt with the horns and show a tendency to lick other animals. They bellow more than common and the sexual desire is increased. Paralytic symptoms are manifested early in the disease, and the animal may fall when moving about. They soon present a gaunt, emaciated appearance.