26 PHYSIOLOGICAL AND THERAPEUTIC ACTIONS 



increasing intestinal secretion and peristalsis ; the irritant is 

 thus swept away, and spasm and pain are removed. A dose 

 of physic prescribed for a horse with itching and swollen 

 legs produces the physiological effects of emptying the 

 bowels, and clearing the body of irritant waste matters with 

 the curative result of relieving or removing the itching and 

 swelling of the limbs. Hunting horses frequently, after a 

 hard day, have stiff limbs, with puffy joints and tendons ; 

 diligent hand-rubbing and subsequent bandaging mechani- 

 cally and physiologically stimulate the activity of the local 

 circulation, with the therapeutic effect of restoring the parts 

 to their normal state. All the physiological actions pro- 

 duced by medicines may not be favourable to the curative 

 result desired, but subsidiary, useless, or harmful effects may 

 be diminished or neutralised by judicious selection and 

 combination of remedies. Some medicines are chiefly local 

 and direct in their action. A strong acid applied to the 

 skin irritates and, it may be, destroys it. A hot fomentation 

 or poultice in contact with a painful surface soothes it, and 

 relieves local congestion and pain. The primary action of 

 local irritants is frequently followed by secondary and 

 remote effects. In sore throat the application of a blister 

 directly irritates and inflames the skin, and reflexly, or 

 through the nervous system, it relieves congestion and pain 

 of the respiratory membrane. In horses a large cantharides 

 blister, used for its local effect, may, owing to absorption 

 of the active principle of the fly, occasionally produce 

 febrile symptoms, and congestion of the urinary passages 

 by which the irritant is excreted. 



The general effects of most medicines are only produced 

 when they enter the blood, and the more rapidly a medicine 

 enters the circulation the more immediate and powerful are 

 its effects. The short time required for absorption, distribu- 

 tion, action and elimination is well illustrated in the rapidly 

 fatal effects of such poisons as prussic acid and strychnine. 

 Yellow prussiate of potash injected into the trachea was 

 detected two minutes later in the jugular vein (Colin) ; 

 injected into one of the jugular veins of a horse it appeared 

 in the other in twenty-five seconds, and in a few minutes 

 was exhaled from the mucous and serous membranes 



