To enumerate all the drugs which act directly or indirectly upon the skin, when applied externally or administered internally, would be to name many of the agents in the Pharmacopoeia. It will be understood, therefore, that this title is given to such as have a special or marked action upon the integument of the particular animal under consideration.

In the portion of this work dealing with the physiology of the skin, the great difference between human skin and that of the horse has been alluded to.

While the administration of certain drugs may be depended upon to have an almost certain effect in producing sweating in man, no such pronounced effect is seen in horses. "There is no drug", says Col. Smith, who has investigated the subject very thoroughly, "which produces sweating in horses." It must be understood, however, that this remark applies to visible perspiration. We cannot well believe that the insensible perspiration which is always going on is not materially influenced by drugs whose action upon the general condition of the skin has been well known to practical horsemen for ages. (See Alteratives.)

The importance of drugs acting upon the skin when externally applied is frequently alluded to in other chapters, as when blisters are applied over the seat of inflamed organs and parts of the body suffering from various forms of injury.

Drugs which are believed to increase the amount of sweat are called sudorifics or diaphoretics. Among them may be mentioned, as being most in favour with veterinary practitioners, acetate of ammonia, bicarbonates of potash and soda, camphor, ipecacuanha, antimony, and Dover's powder, which is a combination of opium, ipecacuanha, and potash sulphate.

Pilocarpine is said to have a diaphoretic action by some observers, but it is not in general use.

The want of a drug in veterinary practice which will make a horse sweat is not so much felt as medical practitioners sometimes imagine, since the equine patient can generally be made to perspire by the use of additional clothing and an increase in the temperature of the stable.