9O ASPHYXIA, 



cardiac and vascular centres. Overaction of the heart is 

 prevented by the influence of the resulting augmentation 

 of intra-cranial pressure on the heart centre in the medulla 

 oblongata ; over-constriction of the vessels by the influence 

 of the resulting increase of endocardial pressure through 

 the depressor fibres of the vagus on the vaso-motor 

 centre. 



Death by Asphyxia. When respiration is suddenly pre- 

 vented, either by complete occlusion of the air passages 

 or by submersion, the circulation of unarterialized blood 

 in the brain gives rise to disturbances of the actions of 

 the respiratory, cardiac, and vascular centres, which in a 

 few minutes bring respiration and circulation to an end. 

 The process is divisible into two stages. The first stage is 

 characterized by rapidly increasing hyperpncea, contraction 

 of the arteries, increased arterial pressure, and acceleration 

 of the circulation ; towards its close the expiratory move- 

 ments become more forcible than the inspiratory, and as 

 insensibility approaches, pass into " expiratory convul- 

 sions " of short duration. In the second stage the animal 

 is entirely unconscious ; the pupils are first contracted, 

 then dilated, while the convulsive expirations give place to 

 violent inspiratory gasps. After these have ceased the 

 heart continues to beat, at first slowly, then with increased 

 frequency but diminished effect, until at last the arterial 

 pressure has sunk to zero, and the whole of the blood has 

 collected in the venous system and in the cavities of the 

 heart. The duration of the process is mainly dependent 

 on the quantity of air contained in the respiratory cavity 

 at the moment of occlusion of the air passages, on the 

 relative quantity of blood which the animal possesses, on 

 its age, and on the activity of its chemical processes. 



Influence of the nervous system on the Temperature of the 

 body. The influence of the nervous system on the heat- 

 producing processes, by which the constancy of the tem- 

 perature of the body is maintained, is as yet unknown. 



