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[N. S. Vol. XXIX. No. 743 



the possible strain which may at times be 

 placed upon the heart and arteries, but 

 they do not give us the knowledge we 

 should have of the pressure conditions 

 during fatigue. It is clear enough that in 

 the increased output from the heart and 

 the probable constriction of the arterioles 

 of the splanchnic and other internal or- 

 gans pressor factors are introduced, while 

 in the dilation of muscular and cutaneous 

 arterioles depressor factors are introduced ; 

 through the changes of thoracic aspira- 

 tion and tlie rhythmic pressures on the 

 bloodvessels of the working muscle and 

 moving joints, arterial pressure must also 

 be influenced, the exact direction of the 

 influence probably differing with the na- 

 ture of the exercise and the condition of 

 the organism. Finally, where very rapid 

 rhythmic or sustained contractions are 

 made, the blocking of the circulation 

 through the muscles must exert a marked 

 depressor influence. The net result must 

 be the algebraic sum of these pressor and 

 depressor influences and we are prepared 

 to find, as we actually do, considerable 

 variations of result. Thus Zuntz and 

 Hagemann° found in the horse a slight 

 fall of mean pressure, but sometimes a 

 slight rise with moderate work. In the 

 dog, on the other hand, Tangl and Zuntz* 

 always found a rise of from 20 to 30 mm. 

 of mercury with active exercise; but 

 when the dog was made to run very 

 rapidly in the treadmill so that distinctly 

 labored breathing developed, enormously 

 high mean pressures of 275 mm. of mer- 

 cury were recorded. In the latter case, 

 the relaxation period of the muscle was 

 probably not long enough to permit the 

 blood to flow through in any quantity, so 

 that the great muscular outlet from the 



' Zuntz and Hagemann, " StofFwecliael des Pfer- 

 des," 387 foil, Berlin, 1898. 



"Tangl and Zuntz, Pflilger's Archiv, LXX., 554, 

 1898. 



aorta was temporarily blocked off. These 

 direct measurements, however, suffice to 

 show that moderate muscular activity 

 causes only a slight change of mean ar- 

 terial pressure and that change usually 

 an increase of from 20 to 30 millimeters of 

 mercury; but that certain forms of mus- 

 cular activity may result in pressures 

 which must be looked upon as distinctly 

 dangerous. 



Upon man I would next call attention 

 to Bowen's'^ very careful measurements of 

 systolic pressure, during work on a sta- 

 tionary bicycle, the work being described 

 as "just vigorous enough to satisfy the 

 needs of a healthy man who is not in train- 

 ing for athletics." He found that the 

 systolic pressure rose from 130 mm. of 

 mercury to a maximum of 180 mm. within 

 the flrst five or ten minutes; after this 

 there was a fall to a plateau of 165 or 170 

 mm., or even a continuous but gradual fall 

 throughout the thirty-five minutes of the 

 work. After the cessation of the work 

 there was a sudden fall to or even below 

 the normal, followed by a return to normal 

 within ten minutes. Those interested in 

 the subject will find Bowen's paper very 

 suggestive. 



Lastly I should mention McCurdy's* 

 measurements of systolic pressure during 

 the maximal effort of the ordinary gym- 

 nasium test of strength of legs. The pres- 

 sure was first raised in the brachial arm- 

 let to 500 mm. of mercury, or thereabouts, 

 and then rapidly lowered during the 

 effort until the radial pulse could be felt. 

 This method would give somewhat low 

 records for systolic brachial pressure, but 

 even then pressures of from 175 to 265 

 mm. of mercury were recorded. The form 

 of effort reproduced the conditions of 



' Bowen, American Journal of Physiology, XI., 

 59, 1904. 



' McCurdy, American Journal of Physiology, Y., 

 95, 1901. 



