34 METABOLISM DURING WALKING. 



subject walking which were taken by the writer with a string galvano- 

 meter. These were made largely to test the possibilities of this method 

 for determining the pulse-rate during muscular work. While condi- 

 tions did not permit at that time the collection of any considerable 

 amount of data, the method was shown to be practicable. The results 

 here reported were first obtained by means of a Bock-Thoma oscillo- 

 graph and later by the use of a Cambridge string galvanometer, 

 somewhat modified, especially as to the registering apparatus. 



OSCILLOGRAPH. 



The Bock-Thoma oscillograph 1 was equipped with four filaments, 

 but only one was used. This was of platinum with a diameter of 

 0.0025 mm. and a resistance of 5,000 ohms. In place of the regular 

 time equipment, a Jaquet graphic chronometer was employed, the 

 pointer of which interrupted a beam of light in front of the camera- 

 slit. As only the pulse-rate was desired in these experiments, the 

 speed with which the photographic paper was supplied to the camera 

 was reduced to approximately 25 cm. per minute. At this speed each 

 pulse-beat could be easily counted on the record and the distance 

 between the second marks could be readily estimated to tenths. 



It was found difficult at that time to obtain photographic paper of 

 American manufacture that was sufficiently sensitive for use with this 

 instrument, while the paper originally supplied with the instrument 

 was expensive and did not keep well. Ultimately a satisfactory 

 European paper was obtained. The greatest difficulty, however, 

 was found with the filaments of the oscillograph. These were exceed- 

 ingly delicate and liable to damage. Finally, when war conditions 

 made it impossible to replace broken filaments, the use of the oscillo- 

 graph was discontinued. A typical record of the pulse-rate as ob- 

 tained with this instrument is given in C, figure 8. 



CAMBRIDGE STRING GALVANOMETER. 



In the fall of 1916 a Cambridge string galvanometer, which had 

 previously been used in the psychological work of the Laboratory, 

 was employed for measuring the pulse-rate of the subjects in the walk- 

 ing experiments. For this purpose a camera of the so-called Morse 

 type 2 was substituted for the camera provided with the Cambridge 

 instrument. This apparatus was so changed that the mechanism 

 supplying the photographic paper to the camera was driven by a 

 1/80 h. p. motor of 2,200 r. p. m., equipped with a rubber friction 

 drive in place of the usual worm and gear, also with a suitable set of 

 reducing pulleys. The speed with which the paper was being fed to 

 the camera was indicated by a pointer fixed to the feed-shaft revolving 

 over a graduated dial. By means of a hand rheostat, the speed of the 



'Groedel, Theo. and Franz, Deutsch. Archiv f. klin. Med., 1912, 109, p. 52. 

 s Manufactured by Edelmann and Sohn, Munich, Germany. 



