106 Dr. W. Marcet. 



carry a heavy weight, or to run up hill pursuing another person, or 

 to ride a bicycle up hill, or in any other form, care being taken to 

 keep the muscles absolutely at rest, when the result was invariably 

 an increase in the volume of air expired, as shown in the chart. On 

 suddenly dropping the influence of the will, and relapsing into the 

 usual state of mind, a slight reaction was visible on the chart re- 

 calling forced breathing. The line, however, is straighter, and 

 nearly free from the after rise observed in forced breathing, thus 

 exhibiting a slight tendency to the form of curve peculiar to breathing 

 under exercise. 



Let us now inquire more closely into the present form of breathing. 

 The moment the will is applied, as stated above, there is an increase 

 in the volume of air breathed. What is the reason of this pheno- 

 menon ? It must result from one of two different causes or from 

 both either an increased demand of oxygen by the blood, or the 

 acquired habit of breathing more air while under an exercise which 

 is itself controlled by the will. The increased action of the respiratory 

 muscles when influenced by an effort of the will is absolutely auto- 

 matic ; there is no strain, no effort of any kind recalling forced 

 breathing. Together with a greater volume of air breathed per 

 minute we observe a marked increase of C0 2 produced and expired 

 an increase which amounts to a mean of 2O9 c.c. per minute. These 

 20'9 c.c. of C0 2 can only be due either to increased labour in the act 

 of breathing, or increased combustion from the effect of the will, or 

 to both these causes. The increased respiratory labour which is un- 

 conscious and unattended with fatigue must be very slight, and to 

 my mind cannot account for 2O9 c.c. of C0 2 per minute ; moreover, 

 if the fact be taken into account that the increased volume of air 

 breathed under an effort of the will points distinctly to a demand 

 of oxygen from the air by the blood, and an increased production of 

 CO 2 which has to be emitted, we shall be more and more convinced 

 that volition (powerfu)ly exerted) is productive of carbonic acid. 



If we now turn our attention to the graphic illustration of breath- 

 ing under a strong exertion of the will, we observe that the apncea 

 is somewhat less marked than in forced breathing, the curve 

 straightening and thus approaching that of respiration under mus- 

 cular exercise. 



Taking into account the whole of the above considerations, it 

 appears to me that we are justified in concluding, as it were from 

 circumstantial evidence, in the absence of direct proof, that oxygen 

 is absorbed and carbonic acid formed in the body from the mental 

 effort of the exertion of the will. A remark falls from Dr. Vaughan 

 Harley, in a recent paper on The Value of Sugar and the effect of 

 Smoking on Muscular Work"* in keeping with the foregoing ob- 

 * ' Journal of Physiology,' 1894. 



