96 Dr. W. Marcet. 



though not from excessive oxidation, with the exception of a small 

 amount due to the extra work of the respiratory muscles. 



3rd. Respiration under exercise increased volumes of air inspired 

 and expired in a given time with an expiration of C0 2 in excess of the 

 C0 2 expired in repose, and unattended with fatigue. At the same time 

 there occurs an increase of the C0 3 in store in the blood, which takes 

 place with a certain regularity during the first fifteen or eighteen 

 minutes after exercise has begun, and is irregular afterwards. This 

 excess of stored up C0 2 is given out as soon as exercise is followed by 

 repose. 



4th. The fourth form of breathing is under the influence of volition, 

 when exerted in a person's imagination towards a powerful muscular 

 exertion, while the muscles are in a perfect state of repose. This 

 form of breathing exhibits the characters of forced respiration and 

 respiration under exercise. 



These four different forms of breathing have received special 

 attention, and will, collectively, be found to include every variety of 

 respiration. They have been recorded graphically in the charts which 

 accompany the present paper. By means of a drum revolving regu- 

 larly by clockwork, and of a style at the end of a rod fixed to the 

 summit of the bell-jar into which the air was expired, tracings were 

 obtained on lithographed charts. The abscissae on the charts indi- 

 cate the litres of air expired, and the ordinates the minutes through 

 which the experiment was continued. 



The air expired was analysed, either for the determination of its 

 G0 2 alone, or of its C0 2 , 0, and N" ; the volume of nitrogen obtained 

 yielded by a simple proportion the volume of air inspired. 



I shall now beg to give an account of my inquiry on these different 

 forms 'of respiration. 



list. Normal Breathing in the Stale of Repose. 



The methods adopted in the present work have been fully described 

 elsewhere ; as time elapsed improvements were introduced, and 

 this last year the bell-jars used for collecting the expired air, instead 

 of being exactly balanced as in former experiments, had their 

 counterpoise charged in such a way as to give a slight ascending 

 motion to the receivers when in free communication with the atmo- 

 sphere, the speed they acquired being rather less than would be 

 produced by the rush of air owing to the expiratory effort. Thus, 

 the respiration was unattended with the unconscious strain necessary 

 to raise the bell-jar while perfectly balanced. This effort, although 

 unnoticed at the time, had a slight tendency to bring on after a 

 while a sensation of fatigue in the respiratory muscles, and pro- 

 bably to increase, though to a very small amount, the volume of 



