In some nervous animals, especially high bred horses and dogs, there is undoubtedly an idiosyncrasy which shows itself in a special susceptibility of the nervous system. In such animals an exposure to cold or wet, or the presence of a local irritant which would have been without effect under other circumstances, lights up the nervous disorder and produces an explosion, it may be as spasm or it may be as nervous pain. Animals that are kept under the best care, that are least accustomed to exposure and neglect, that are highly fed, and maintained in high spirits and are impatient of control are more susceptible than those that become inured to change and exposure, yet are kept in moderately good condition. On the other hand the subject which has become debilitated by overwork, underfeeding, exhausting disease, or the generation in the system of some depressing poison is likely to show a similar nervous susceptibility, so that at the two extremes of plethora and nervous susceptibility, on the one hand, and anæmia and neurasthenia on the other, we find a corresponding tendency to nervous disorder under comparatively slight causes. Thus it happens that a drink of ice cold water, an exposure to a cold blast or a drenching rain or a heavy night dew may seem to be the one appreciable cause of the trouble. If the animal has been perspiring and fatigued the attack is more likely to occur. In other cases a slight indigestion unattended by impaction or tympany, or the ingestion of an irritant which on another occasion, or in another animal would have been perfectly harmless, will induce a violent nervous colic. In some instances the attack is supposed to be of a rheumatic nature the causative action of the cold giving color to the theory. _Symptoms._ The attack usually comes on suddenly especially if it has followed on a drink of cold water or a cold exposure.