THE FOUR STAGES OF ANAESTHESIA 77 



one to three minutes, but is shortened when the drug is 

 given quickly in full doses. 



II. The narcotic stage is marked by paralysis of the 

 motor centres, the voluntary muscular system gradually 

 becomes relaxed, the force and volume of the pulse are 

 lowered, the functions of the higher brain centres are im- 

 paired, but reflex functions are slightly if at all affected. 

 This stage, usually reached in less than five minutes, is that 

 suitable for anodyne and antispasmodic effects, and for 

 moderating violent and irregular labour pains. 



III. The anaesthetic stage exhibits complete muscular 

 relaxation, unconsciousness, and insensibility ; the fre- 

 quency and force of the pulse are decreased, although it 

 remains quite regular ; respiration is regular but somewhat 

 shallow, the functions of the cerebrum and spinal cord are 

 paralysed, the oculo-palpebral reflex is impaired or abolished, 

 the pupil is slightly contracted, but the centres of the 

 medulla presiding over respiration and heart action are only 

 slightly affected. This complete insensibility may be safely 

 maintained for an hour or two by small doses of the anaes- 

 thetic, and is the condition requisite for the performance of 

 serious surgical operations. 



IV. The paralytic stage occurs when the functions of the 

 medullary centres are abolished. It includes two distinct 

 phases suspension of respiration, and subsequently suspen- 

 sion of cardiac action. Implication of the respiratory centre 

 is indicated in animals by irregular sighing or shallow 

 breathing, with long pauses between the respiratory move- 

 ments. This is partly due to direct depression of the medul- 

 lary centre and also to anaemia of the centre owing to failing 

 circulation. Up to this point the animal is in no serious 

 danger. But if anaesthesia is further pushed, the heart 

 centre is paralysed, the pulse beats very quickly then stops, 

 blood pressure falls to zero, and usually within two minutes 

 heart action also ceases. 



The action of anaesthetics was very fully elucidated by two 

 series of investigations undertaken at the instance of the 

 Nizam of Hyderabad. The first, made in the spring of 1888, 

 under the supervision of Surgeon-Major Lawrie, comprised 

 141 experiments, chiefly on dogs ; while the second, made 



