66 THE APPLIED PHYSIOLOGY 



still, by bleeding, can only defeat Nature in her 

 efforts to keep the patient from fatal syncope. 

 Lumbar puncture would give relief, but unfortunately 

 the pressure is usually above the tentorium, and in 

 this region it is scarcely at all affected by lumbar 

 puncture. Nevertheless, it is always worth a trial. 



After less severe injuries to the head, such as con- 

 cussion, the blood-pressure is usually subnormal. 

 This is presumably due to the inability of the vaso- 

 motor centre, which shares in the injury, to recover 

 its full control of the arteries in the systemic circula- 

 tion. Regular observation of the blood-pressure in 

 these cases is a valuable clinical guide to treatment. 

 Absolute quiet in bed and a milk diet should be 

 insisted on till the blood-pressure is restored to the 

 patient's normal, and if any liberty granted is 

 followed by a fall in the pressure, it will be necessary 

 to proceed more slowly. By observations on these 

 lines we may hope to avoid the headaches and 

 nervous prostration which so often follow head 

 injuries. 



THE PULMONARY CIRCULATION. 

 HAEMOSTATICS. 



The circulation through the lungs also calls for 

 special treatment, because here again the vessels do 

 not respond to the impulses which elsewhere cause 

 vasoconstriction. It has been exhaustively argued 

 whether the lungs have any vasomotor nerves, and 

 the answer seems to be in the negative (though nerve 

 fibres certainly run on the vessels). Adrenalin is 

 powerless to constrict the arteries of the lung and 



