DIGITALIS. 311 



confined to the circulatory organs, the other parts being 

 chiefly affected secondarily. Both the heart and vessels are in- 

 fluenced "by the drug, the action of which occupies four stages, 

 the first stage being shortened and the other stages more marked 

 as the dose is increased. In the first jstage, the heart falls in fre- 

 quency (say to fifty per minute), from"stimulation of the vagus in 

 the heart and medulla ; and beats with increased force, from sti- 

 mulation of the intrinsic ganglia. Therewith the arterial pres- 

 sure rises, from the increased cardiac force, and from excitation 

 both of the vaso-motor centre and vaso-motor nerves. The result 

 of all this is that the ventricles are well filled (diminished fre- 

 quency, i.e. lengthened diastole) ; the ventricles are thoroughly 

 emptied (increased force) ; the arteries are thus well filled ; and 

 they are kept filled (vaso-motor action.) The condition is that 

 of a perfect circulation, which empties the veins and fills the 

 arteries. 



In the second stage, the state of the heart remains un- 

 changed, but the vaso-motor apparatus of the renal arteries are 

 rather suddenly depressed ; these vessels are relaxed ; and the 

 force of the circulation is thus thrown upon them, that is on 

 the glomeruli. The result is increase in the excretion of 

 urinary water. 



In the third stage, the heart rises in frequency, from de- 

 pression of ~th~e vagus, and probably some irritation of the 

 sympathetic (accelerator) fibres; and loses force, from com- 

 mencing exhaustion of the intrinsic ganglia and muscle. At the 

 same time the arterial pressure falls, from the weakening of the 

 heart, and from depression of the vaso-motor apparatus, which 

 spreads from the kidney, where it commenced, to the other 

 peripheral arterioles. Thus the circulation begins to fail. 



In ihefourtJ^stage, the action of the heart becomes irregu- 

 lar, infrequent, andweak, from failure of the ganglia and 

 myocardium; and is finally arrested in diastole. Therewith 

 the blood pressure gradually sinks to zero, from loss of cardiac 

 force and complete paralysis of the vessel walls. Death occurs 

 by general circulatory failure. 



Respiration fails at last, but only through the circulation. 

 The voluntary muscles are paralysed through failure of their 

 blood supply. The uterus is said to be stimulated by moderate 

 doses. The body temperature is briefly raised through increased 

 vigour of the circulation ; it is then lowered by the increased 

 blood-flow in the skin ; and falls still more in the last stages, in 

 an irregular uncertain way, from causes still obscure. Digitalis 

 is thus a refrigerant. The central nervous system is only secon- 

 darily affected through the blood supply. Headache, giddiness, 

 disturbance of sight and vision are frequently induced by 



