236 A MANUAL OF PHYSIOLOGY 



movements and a fall of blood-pressure through vaso-dilatation 

 (Brodie). 



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 to 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 unweakened 

 (Fig. 73, p. 175). 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 strychnine, 

 in birds and in alligators, movements, apparently respiratory, 

 have been seen after destruction of the brain and spinal bulb. 

 In adult cats, when the functions of the brain, medulla, and 

 cervical cord have been abolished by occlusion of their vessels, 

 similar movements of the thoracic and abdominal muscles may 

 be seen, but they are not sufficient for effective respiration. 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 respira- 

 tion than that of a mere conductor of nerve impulses ; and it is 

 not justifiable to assume the existence of automatic 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 

 (or vago-sympathetics) in the neck. In certain animals, at least, 

 this operation is incompatible with life. In the rabbit, as a rule, 

 death takes place in twenty-four hours. A sheep may live three 

 days, and a horse five or six. Dogs often live a week, occasionally 

 a month or even two, and in rare instances they survive indefinitely. 

 The most prominent symptoms (in the dog), in addition to the 

 marked and permanent slowing of respiration, quickening of the 

 pulse and contraction of the pupils, are difficult deglutition, accom- 

 panied by frequent vomiting and progressive emaciation. The 

 appetite is sometimes ravenous, but no sooner is the food swallowed 

 than it is rejected ; and this is particularly true of water or liquid 



