202 A TEXTBOOK OF PHYSIOLOGY 



renalin furnished by the adrenal glands. Adrenalin maintains the 

 tone of the sympathetic system. 



By sudden fright in the standing posture the respiration is often 

 arrested, the vaso-motor tone inhibited, and syncope induced by the 

 blood sinking into the abdomen. Recovery from syncope is brought 

 about by the assumption of the horizontal position or compression 

 of the belly. When the compensatory mechanism is entirely lost, 

 the circulation is only possible in the recumbent position, and life is 

 at its lowest ebb. Among the anaesthetics in common use, chloroform 

 stands prepotent as a drug which has the power to abolish the com- 

 pensatory mechanism. Chloroform causes cardiac dilatation (Fig. 104), 

 weakens the respiration, and makes flaccid the abdominal muscles. 

 The effects of ether are not so serious (Fig. 105). 



A useful clinical guide to the condition of the compensatory 

 mechanism in man is afforded not only by the pressure in the brachif 1 

 artery, but by the rate of the pulse on change of posture. If the heart 

 greatly accelerates on rising from the horizontal to the vertical position, 

 the mechanism is deficient. 



