PHYSIOLOGY OF MOUTH-BREATHING APPLIANCES. 177 



The effect of horizontal walking upon the blood-pressure is there- 

 fore not large, even at the highest speeds here reported, as compared 

 with the increases in blood-pressures known to occur with other forms 

 of work, such as those found in exercise with dumb-bells by Cotton, 

 Rapport, and Lewis. 1 There is, however, a point above 80 meters per 

 minute at which the effect upon the blood-pressure of the speed of 

 walking may be clearly noted. 



EXPERIMENTS WITH GRADE WALKING. 



As explained in the section on methods (p. 29), the treadmill was 

 constructed with two long screw members attached to the head, by 

 means of which the front of the treadmill could be raised so as to give 

 angles of elevation as desired up to approximately 45. Aside from 

 the fact that under these conditions the subject walked on a pre- 

 determined incline, the details of the grade-walking experiments were 

 in no respect different from those with horizontal walking. As the 

 degree of elevation increased, less power was needed to drive the tread- 

 mill, and at the highest grades the weight of the subject alone would 

 have been sufficient to cause the speed to increase continuously. To 

 control this and thus secure uniformity in speed, an adjustable brake 

 was placed on the shaft of the motor. (See p. 29 and fig. 1, p. 19.) 

 This tendency to an increase in speed during the experiment was a 

 frequent source of trouble, and careful attention was required to pre- 

 vent any gradual alteration in speed from unexpectedly developing. 



The results of the measurements in the grade-walking experiments 

 are given in detail in tables 13 to 16a (pp. 69 to 89), in which the values 

 are chronologically arranged for all of the experimental periods with 

 every subject. Before discussing the results of these experiments, a 

 consideration of the method used for studying the respiratory exchange 

 is desirable, more especially the use of the mouthpiece under the special 

 conditions of grade walking. 



PHYSIOLOGY OF MOUTH-BREATHING APPLIANCES. 



While the mouthpiece in its various forms has been extensively used 

 for respiration experiments with the subject lying or standing or walk- 

 ing, there has been much criticism by investigators as to the physio- 

 logical effects of using such an appliance. Some go so far as to state 

 that it is physiologically impossible for a man to breathe normally 

 through a mouthpiece. This extreme opinion is held by only a few 

 workers on the respiratory exchange. With walking experiments, 

 however, the question might fairly be raised whether the use of the 

 mouthpiece would affect the results obtained, more especially during 

 the severe exercise of grade walking, when the oxygen consumption 

 would necessarily be very considerable and the pulmonary ventila- 



'Cotton, Rapport, and Lewis, Heart, 1917, 6, p. 269. 



