196 PHYSIOLOGY FOR DENTAL STUDENTS. 



blood during gas anesthesia, stimulates the vasoconstrictor cen- 

 ter, producing a rise in blood pressure. The narcotic action of 

 the gas depresses the inhibitory effects of the vagus cardiac cen- 

 ter on the heart. The heart is therefore quickened and tends 

 still further to increase the blood pressure. For these reasons it 

 is not wise to use nitrous oxide in the case of elderly patients 

 with weakened sclerosed arteries, or in the case of those suffering 

 from cardiac disease. When oxygen is given along with the 

 nitrous oxide the asphyxial phenomena are reduced. 



Cocain. The effect of cocain injections on the circulation are 

 both central and peripheral, and vary according to the dose and 

 the individual susceptibility. Very small doses generally cause 

 a slight fall in blood pressure, due to slowing of the heart from 

 stimulation of the vagus. The vasomotor center is likewise stim- 

 ulated, but the resulting vasoconstriction does not compensate 

 for the fall in pressure caused by the decreased action of the 

 heart. Moderate doses depress the vagus function and increase 

 the heart rate, which, together with the vasoconstrictor stimula- 

 tion observed in the case of the smaller doses, causes a marked 

 rise in the blood pressure. Large doses paralyze the vital centers 

 in the medulla, and a great fall in blood pressure results. With 

 small doses the respirations are accelerated, but in fatal doses 

 the respiratory center (see p. 219) is paralyzed and death ensues. 





