These are practically divided into two classes - namely, those which cause the vessels to contract and consequently permit a smaller amount of blood to pass through them, and those which dilate them and permit of a greater quantity to flow through them. When a portion of the body is in a state of active inflammation, we employ the first class of remedies. In veterinary practice we have frequent recourse to the cold douche, cold lotions, and bandages, ice, etc, for the reduction of inflamed joints and to control haemorrhage.
In the second class we place hot fomentations and poultices, mustard and warm embrocations, as their effect is to produce temporary dilatation of the vessels of the skin and enable the blood within to distend them to their greatest capacity. In this way mustard applied over the chest walls in pulmonary inflammations gives relief to the vital organs by diverting blood from them to the surface. Stimulating the legs with liniments, and hand-rubbing, has the same influence in bringing about a more general distribution of the blood, which in internal inflammation is centred upon some more important organ or organs. In addition to the methods of relaxing superficial vessels as illustrated above, there are also remedies which have a like effect upon internal organs, and by bringing more blood to the part, increase their physiological activity. Among those used in veterinary practice may be mentioned ginger, capsicum, pepper, grains of paradise, and some others of doubtful value employed in the treatment of impaired digestion. Drugs which relax the vessels of the skin, as alcohol, nitrate of potash, acetate of potash, and nitrous ether, produce a sensation of warmth for a short time, and this is why alcohol is popularly believed to increase the warmth of the body, although it has already been shown that its ultimate effect is to reduce temperature.
Fig. 429. -Ergot of Rye.
1, Spanish ergot. 2, Russian ergot.
The most recent and effectual remedies for dilating the blood-vessels all over the body are the nitrate of amyl and nitro-glycerine. The former has to be inhaled to produce its effect, and the latter is given internally. They are used for heart spasm (angina pectoris), and in asthma, broken wind, and convulsions. In poisonous doses paralysis of both motion and sensation results, and death by cessation of respiration.
We have now to consider those drugs which are credited with producing the opposite effects upon bloodvessels.
Ergot of Rye (fig. 429) is one of the most active drugs in causing contraction of the small blood-vessels in man and some of the domesticated animals; but its action upon horses is uncertain, and even in large doses its effects are not so marked as upon dogs. It probably has some medicinal value, and is therefore mentioned in this connection. It is thought by some to be the cause of abortion when taken as ergotized grasses, but experiments in 'which pregnant animals have been dosed with large quantities do not bear out the theory. It is given to mares after parturition, with a view to induce contraction of the womb, and has been recommended for inflammation of the coverings of the brain and spinal cord.