536 DIGITALIS 



decomposition, especially when exposed to high tempera- 

 tures, and several of these products are convulsants like 

 picrotoxin. 



ACTIONS AND USES. Digitalis is a topical irritant and 

 contractor of muscle, especially of the unstriped variety. 

 Medicinal doses are vascular and cardiac stimulants and 

 tonics, and are prescribed to increase the force and co- 

 ordinating power of the heart, and relieve congestion of 

 veins and capillaries. They are diuretic. In healthy 

 animals small doses of digitalin lower rectal temperature 

 from -^yths to ^ths of a degree. Large doses are muscle 

 poisons : they contract spasmodically and even tetanically 

 the heart and other muscles, and kill usually by cardiac 

 paralysis. 



GENERAL ACTIONS. Digitalis, in contact with living 

 tissues, is an irritant. Injected under the skin or into the 

 trachea it irritates and inflames. Placed in the mouth, 

 besides a sensation of bitterness, it causes salivation and 

 redness. Introduced into the stomach and bowels, it in- 

 duces irritation and nausea ; in carnivora, vomiting, colic, 

 and diarrhoea. It is absorbed slowly, often taking several 

 hours to produce its effects, and contracts muscular fibre, 

 notably of the heart and arterioles. It also stimulates the 

 medulla and so increases the inhibitory action of the vagus. 

 Properly regulated doses thus strengthen and prolong the 

 cardiac diastole, both auricles and ventricles are more fully 

 dilated, systole is more vigorous, and consequently the heart 

 is more perfectly emptied. The muscular fibres of the 

 arterioles have their tonicity increased. Blood-pressure 

 accordingly is raised. Such doses, while increasing the 

 volume of the pulse, diminish the pulse-rate of healthy 

 horses three to five beats, and of dogs ten to fifteen beats 

 per minute, and these effects last from six to twelve hours. 

 The action on the heart is more notable on the dog and 

 sheep than on the horse and ass. 



The action on the circulation may be divided into the 

 following stages : 



1. Medicinal doses cause a fuller stream of blood to be 

 thrown into the circulation, blood-pressure rises, the pulse is 

 slowed, but increased in volume. These effects depend on 



