100 Dr. ^ T - Marcet. 



expired into bell- jars with weighted counterpoise, as previously ex- 

 plained. With the balanced bell-jar there was a slight amount of 

 work done which gave the breathing a degree of steadiness wanting 

 with the counterpoise weighted ; in the former experiments the very 

 slight, though imperceptible, effort to raise the bell-jar gave regu- 

 larity to the respiratory function. It must be recollected that during 

 the day time, sitting perfectly quiet in an arm-chair, from a quarter 

 of an hour to an hour, is altogether unnatural in ordinary life. We 

 are always in a state of activity, and therefore the slight effort to 

 raise the balanced bell- jar is perhaps more consistent with the ordin- 

 ary functions of life than breathing perfectly freely, doing practi- 

 cally no work, indeed breathing much as we do at night in bed and 

 during sleep. I therefore believe that the irregularity in the present 

 figures obtained for the composition of expired air does not militate 

 in any way against my former conclusion. 



The next subject for our consideration will b'e 



Forced Breathing. 



Let us follow the different stages of this form of respiration. The 

 person under experiment is resting in the recumbent posture and 

 perfectly still, he then takes a succession of deep nasal inspirations 

 while expiring through the mouth into one of the bell- jars. After a 

 certain time, say one, two, or three minutes, he suddenly relapses into 

 natural automatic breathing, and then observes that his respiration 

 subsides for a few seconds into a pause or state of apnoea ; by degrees 

 it returns, shallow and feeble, and then fuller, increasing beyond the 

 normal. If the apncsa has been great, the increase i well marked, 

 but if comparatively slight the increase may be only just perceptible. 

 These characters are invariably met with in every instance of "forced 

 breathing " and are clearly shown by the tracings recorded in the 

 charts. The phenomenon may be conveniently illustrated by means 

 of the following diagram 



The horizontal line AA represents normal respiration, the curve 

 AB the line of forced breathing, the curve BC the collapse in the 

 respiration or apnoea, and gradual return to normal,* which it exceeds 

 in CD, reaching finally the normal in D. 



With reference to the respiratory changes in these three successive 

 stages : In the forced period, or from A to B, much more C0 2 is 



* This return to normal only concerns the C0 2 , the O absorbed takes a longer 

 time to recover. 



