1913] G- O. Higley 391 



After the " normal " rate o£ excretion at rest had been de- 

 termined, the subject began forced breathing at a predetermined 

 rate, continuing this for a minute or so until the curve of carbon 

 dioxide excretion had apparently assumed its permanent direction. 

 At this point, at a signal from the experimenter, the subject began 

 to drive the bicycle as in the preceding experiments. The effect was 

 marked, the new rate of excretion being sharply defined from the 

 normal rate preceding it. The further increase in the rate of excre- 

 tion, after the beginning of work, was now not so prompt in its 

 appearance, and came on more gradually, reaching its maximum 

 after a minute or so, depending on the work. 



In these experiments the latent period of increase due to work 

 was from seventeen to twenty-two seconds. It is evident that as 

 the latent period will vary with the rapidity of the circulation, the 

 rapidity of diffusion, and the rate of work, a more definite figure 

 was not to be expected. 



Shortly after the publication of these results by Bowen and the 

 writer, a communication was received from Prof. N. Zuntz, calling 

 attention to the gradual character of the change in rate of excretion 

 of carbon dioxide after the beginning of work (as already men- 

 tioned) and kindly suggesting a modification of the method of 

 carrying out the latent-period experiments. According to Prof. 

 Zuntz, if the forced breathing were continued for five minutes 

 instead of one minute, as already stated, the blood and tissues 

 would become thoroughly ventilated; the direction of the curve of 

 carbon dioxide would become parallel to that before forced breath- 

 ing began ; and, furthermore, with the beginning of work, the carbon 

 dioxide curve, after the latent period of twenty seconds, would 

 change much more sharply than it did in the published record. The 

 writer accordingly made a series of experiments in which the forced 

 breathing was continued for from five to seven minutes before 

 bicycle work has begun. 



The results of one of these experiments are seen in Plate 4 in 

 which A is the Pneumograph record, Pqrs the carbon dioxide curve, 

 T the Chronograph record, and M the bicycle record. The line 

 Pq'q^'r, as in the previous paper,^ represents the rate of excretion 



* Higley and Bowen : Loc. cit. 



