220 A MANUAL OF PHYSIOLOGY 



absolutely drawn. For it has been shown by a number of observers 

 (MacWilliam, Gaskell and Shore, etc.) that chloroform may paralyze 

 the heart without primarily affecting the respiration ; and, further, that 

 paralysis of the vaso-motor centre, and the consequent withdrawal of 

 blood from the heart and brain to the dilated splanchnic area, may 

 be an important factor in bringing about a fatal result (p. 164). In 

 normal chloroform anaesthesia in man it is easy to demonstrate by 

 the sphygmometer a fall of blood-pressure in the brachial artery of 

 20 to 40 mm. of mercury (Hill). It would seem that death from 

 chloroform may take place either from primary failure of the respira- 

 tory centre followed by failure of the heart, or from primary paralysis 

 of the heart or of the whole vascular mechanism (including the 

 muscular tissue of the heart and bloodvessels and the vaso-motor 

 centre), followed by paralysis of the respiratory centre. Sometimes 

 the respiratory failure and the vascular paralysis may be simultaneous; 

 often one may follow so hard on the heels of the other that it is diffi- 

 cult to decide which is primary and which secondary. The practical 

 lesson is that both the respiration and the pulse must be watched, and 

 with equal care. At a certain stage in chloroform anaesthesia, before 

 it has become very deep, comparatively trifling causes may bring about 

 great and sudden changes in the pulse-rate, owing to the abnormal 

 mobility of the vagus centre (MacWilliam). 



Alcohol in small doses, when given by the stomach or (in animals) 

 injected into the blood, causes stimulation of the respiratory centre 

 and increase in the pulmonary ventilation. In man, this increase 

 usually amounts to 8-15 per cent., but is occasionally much greater. 

 But the limit which separates the favourable action of the small dose 

 from the hurtful action of the large, is easily overstepped. When 

 this is done, and the dose is continually increased, the activity of the 

 respiratory centre is first diminished and finally abolished. In dogs, 

 for instance, after the injection of considerable quantities of alcohol 

 into the stomach, death takes place from respiratory failure, and the 

 breathing stops while the heart is still un weakened (Fig. 57, p. 165). 

 This is the final outcome of a progressive impairment in the activity 

 of the centre, of which the slow and heavy breathing of the drunken 

 man represents an earlier stage. 



Spinal respiratory centres. Although the chief respiratory centre 

 lies in the medulla oblongata, under certain conditions impulses to 

 the respiratory muscles may originate in the spinal cord. Thus, in 

 young mammals (kittens, puppies), especially when the excitability 

 of the cord has been increased by strychnia, in birds and in alligators, 

 movements, apparently respiratory, have been seen after destruction 

 of the brain and spinal bulb. But no proof has ever been given that in 

 the intact organism the spinal cord below the level of the bulb takes 

 any other part in respiration than that of a mere conductor of nerve 

 impulses ; and it is not justifiable to assume the existence of spinal 

 respiratory centres on the strength of such experiments as these. 



Death after Double Vagotomy. Alterations in the rhythm 

 of respiration are not the only effects that follow division of 

 both vagi. In certain animals, at least, this operation is 



