It is kinds of drug that can make animal temporarily lose consciousness and feeling but maintain the life. These drugs, when acting on the central nervous system, shall have minimal impact on the medulla oblongata; there is also a great distance between the amount of anesthesia and the toxic dosage; after stopping the drug, the animals can quickly restore the original physiological function.

Mechanism of action
People still have yet reached consensus on this issue. In recent years, there are several explanations.
① Neural synapse hypothesis; It is recognized that the general anesthetic mainly take effects through inhibiting the central nerve system through blocking the transmission of the nerve impulses in the synapse position.
② the reticular activating system depression theory; It is thought that the general anesthetics has selective inhibitory effect on the brain stem reticular activating system with the peripheral afferent impulses being suppressed, resulting in the phenomenon of anesthesia.
③ Molecular Theory; It is thought that the effect of anesthetics on the central nervous system is mainly determined by the central aqueous phase. Some inhalation anesthetics can promote the formation of hydrated microcrystalline consisting of molecules in the brain fluid with the microcrystalline having a cage-like structure, being able to embed the active side chains and other groups and ions of protein into cages, further blocking its activity, thus interfering with the function of the brain to produce anesthesia. With the continuous increase of the plasma concentrations, the anesthesia first occur in cerebral cortex, followed by subcortical center, then the spinal cord, and finally the medulla oblongata.

inhaled anesthetics
① halothane. It exhibits as colorless liquid with heavy mass but no ignition property. It has chloroform-like odor and burning sweetness. Its narcotic effect is stronger than ether. It has no irritant effect on the mucous membrane with short induction time and do not cause excessive secretions, coughing and throat spasms. It can be used as general anesthetic as well as inductive anesthetics.
② Anesthesia ether; It appears as a colorless, transparent and volatile liquid. It is flammable with specific odor. It is soluble in water and easily soluble in alcohol, grease and so on. When the ether vapor is mixed with air, it is explosive upon coming across fire. After the inhalation of ether by animals, it first suppressed the cerebral cortex with a relatively long induction period. It is suitable for medium and small animal anesthetics.

Non-inhalational anesthetics
①chloral hydrate. It has bitter taste and is pungent and smelly. It can be gradually volatilized in the air; it is easily soluble in water, alcohol, chloroform and ether; it is subject to slow decomposition upon long-term exposure to sunlight; it is also easily decomposed upon heat and alkali condition. It is rapidly converted to trichloroethanol after absorption with strong inhibitory effect on the central nervous system. It is able to inhibit the ascending activating system in the brain stem reticular structure with sedative effect upon small dose, hypnotic effect upon medium dose and anesthetic & anticonvulsant effect upon high-dose. It belongs to equine anesthetic agents.
② barbiturates. Barbituric acid itself has no sedative, hypnotic and anesthetic effect, but when having its 5’ position carbon, 1’ position or 3’ position nitrogen being substituted by different groups or the 2’ position carbon being substituted by sulfur group, it can give various kinds of barbiturates with hypnotic or narcotic effect. Because of the differences in the structure and physicochemical properties of various derivatives, it also behaves differently in the aspects of reaction speed and duration length. According to these features, barbiturates can be divided into long-term barbiturates (phenobarbital, phenobarbital), medium-term (pentobarbital) or short-term or extremely short-term (thiopental) effects drugs. In the field of veterinary, people clinically mostly use medium-term or short-term drugs as basic anesthesia or general anesthetic drugs.
③ pentobarbital sodium;
It appears as white crystalline powder or granules; it is odorless with bitter taste. It is easily soluble in water. It can produce anesthesia or hypnotic effect through inhibition of the ascending reticular activating system in the brainstem structure. It also has inhibitory effect on cerebral cortex, limbic system and the hypothalamus. Amobarbital sodium is the isomer of pentobarbital sodium with its effect, the effect duration and application being similar to pentobarbital sodium. It can be not only used as the anesthetics for small animals, but also used as sedation and basic anesthetic drugs for various animals.
④ Ketamine appears as white crystalline powder and is soluble in water and slightly soluble in ethanol. The brain is capable of blocking the projection of brain contact pathway and thalamus to the neocortex, producing analgesic effect. Because it can temporarily slightly suppress the ascending reticular activating system, the limbic system, and the entire central nervous system, it can cause confusion and even the loss of awareness. Thereby, it is suitable to be used as the basic anesthetics, anesthetics and chemical restraint drugs for horses, cattle, sheep and various kinds of wild animals. Other commonly used clinical inhaled and non-inhaled anesthetic agents also include methoxyflurane, enflurane, anesthesia chloroform, and surital.